Info dump: Some Important Models for Health and Fitness

This is a synthesis of many facts I've learned over the last few years, mainly about metabolism and exercise, [1] that have helped me become much healthier, and might help you. It’s focused mainly on “basic” models that, in my opinion, high school health class ought to cover (though mine emphatically did not). Because of various personality diso ... traits , simply doing what people tell me to do basically never works. In order to achieve things that are easy for many people, I tend to need to (a) learn a lot of information, (b) derive models and theory from that information, and (c) use those models to find actions that work well for me. And anyway, it's more fun this way. So this is written for people who are at least somewhat like me in that respect. It’s not trying to be advice, or to be a comprehensive health guide. It’s an explanation of some of my models, which have let me derive advice for myself. My purpose here is to tell you some things I believe about the world. I'm not trying to tell you about yourself specifically or what will work for you. I do include a section at the end on what I have done over the last year, downstream of the rest of this information (spoiler: I log my food and have targets for protein and energy intake, lift weights in my bedroom, measure my progress, and try to walk a lot. But I do this in ways that are especially easy for me personally). NOTE: All kinds of target ranges and numbers in this document are at least somewhat approximate and will differ depending on context. Some information about my sources and credentials (I have none; I’m just a guy with decent epistemics and unusual YouTube taste) is in a footnote. [2] Nutrition There are two big things going on with the food you eat: energy , and materials . You eat (and drink) because you need energy, and because you need certain materials ("nutrients") to build, maintain, and provide signals to the massively complicated system that is you. Energy The cells that make up your body need energy in order to keep their processes running. Most of this energy is ultimately used via a chemical called Adenosine Triphosphate (ATP). As an analogy, consider the energy you use at home. If you live in a modern apartment, you probably have many different appliances. But most of the appliances in your house run on electricity. The electricity might have come from solar panels or a nuclear power plant, or a gas power plant. Your appliances don't really care about that: they just run on electricity. The processes in your cells get energy by breaking down ATP, like your appliances get energy from the movement of electrons. ATP functions as the energy currency for most of the processes your body runs, like electricity is the energy currency for most of your appliances. But you might notice that nutrition labels don't say "ATP" on them anywhere. This is because your body has its own power plants (including, yes, the "powerhouses of the cell", the mitochondria) that turn other fuel sources into ATP. The food you eat is like the fuel for the power plants: Instead of sunlight or gas, or in some cases ethanol, the power grids in your body can run on carbohydrates, or fat, or protein, or in some cases ethanol. Storage You aren't constantly eating exactly the right amount of fuel for your body. You need to store some energy when you eat, so your body can fill in the gaps later. This storage works like batteries: You charge up when you have access to plenty of energy (food), and then you use it later when needed. Your body does this in a few different ways. The biggest short term energy storage mechanism is called glycogen. Glycogen is a carbohydrate made from glucose, that gets stored mostly in your muscles and liver. It gets used all the time, but especially in short bursts of intense effort like when you're lifting weights or sprinting. That’s a lot of glucose! Image author: Mikael Häggström ; made available under a CC0 license. Glycogen, alongside the water it gets stored with (making it "hydrated glycogen"), weighs about 1 gram per kilocalorie, [3] and your body typically stores between 1 and 3 kilograms (2-7 pounds) of hydrated glycogen. When people talk about changes in "water weight" that happen when you start a diet, a lot of what they're talking about is the water that's used to store glycogen: Most of the weight you lose in the first week of (say) a low-carb diet will typically be from your body using its glycogen stores, with only a little coming from burning fat. The main longer-term energy storage mechanism is fat. Energy stored as fat is much lighter than energy stored as hydrated glycogen: each kilocalorie stored as fat weighs only about an eighth of a gram. But there are limits on how fast energy from stored fat is typically extracted: One widely cited model suggests about 70 kcal per kg (32 kcal per pound) of fat per day at most, though this is an estimate based essentially on napkin math. There's a sense in which many of your other tissues can also be used as an energy store if needed. As we mentioned above, protein can be an energy source, and most of your lean tissues (not including water) are made of proteins. If your body gets relatively desperate for energy (say it needs more energy than it can get from that 70 kcal per kg of fat), it can consume its own tissues to keep everything important running, like tearing down a wooden shed in your back yard to use for firewood in the depths of winter. Energy from food Source Energy (kcal/g; est) Digestible fat 9 Digestible protein 4 Digestible carbohydrate 4 Ethanol 7 Soluble fiber 2 Insoluble fiber 0 Sugar alcohols 0.2-3 Dry glycogen 4 Hydrated glycogen (as stored) 1 Adipose tissue (as stored) 8 Energy per gram from various sources Different fuels give different amounts of energy per gram: Dietary fat gives you about 9 kcal per gram, [4] while protein and carbs provide about 4 kcal per gram. Ethanol is in between, at 7 kcal per gram. These numbers are all rules of thumb: For example, there exist some carbohydrates that give essentially no energy at all (insoluble fiber) and the same is true of some proteins (resistant protein) and even fats (Olestra). People's digestive systems are not identical, which can cause one person to get more or less energy than another from the same food. So: When you eat, your body breaks down the fats, carbohydrates, protein, and ethanol and uses the energy released this way. Some of that energy gets used relatively quickly while some gets stored as hydrated glycogen and fat, to be used later. Generally over hours and days, when you eat more calories than you spend, you'll store the excess as glycogen and fat, and if you eat fewer calories than you spend you'll burn glycogen and fat (and eventually lean tissue like muscle, especially if your dietary protein isn't very high). Note that these things don't just get turned into energy like magic; as they're broken down, they produce material that gets used elsewhere. We'll talk about that in the next section. Nutrients We talked about some nutrients already: Carbohydrates, fats, and proteins are the main sources of energy in the foods you eat. And while your body is using the energy it gets by breaking that stuff down, it is also using the resulting building blocks, and the other components of the food you eat, to build your tissues and equip the processes happening in those tissues. "You are what you eat", very literally. The nutrients we've talked about (fat, carbs, protein) are typically referred to as "macronutrients", while the other things your body needs from food are referred to as "micronutrients". Macronutrients (carbohydrates, fats, and protein) aren't used only for energy. Their building blocks (“monosaccharides”, “fatty acids”, and “amino acids”, respectively) will get used in various places throughout your body. Even though you could meet all your energy needs from any one of these nutrient sources, you need to eat at least some fat (containing "essential fatty acids"), and a more substantial amount of protein (containing "essential amino acids"), to go on living. Not all carbs, or all fats, or all protein, are created equal. As we mentioned above, different specific molecules get digested at different rates, or not at all, and they have effects other than the energy they contain. Protein Proteins are the molecules that make up most of the machinery of life. They can be very large and complicated (figuring out how they fold up and interact is a famously hard problem), but they're made of simpler building blocks called amino acids. Tens of thousands of different proteins in your body are made from just ~20 amino acid building blocks. Image author: SadiesBurrow ; made available under the CC BY-SA 4.0 license . There are 21 amino acids that are used by human biology (one of which is pretty rare, so often you’ll hear there are 20). Some of these amino acids are "essential", meaning that you need to consume enough of them for your body to work. There are nine of these essential amino acids for humans, and six that you need to consume under certain circumstances (they're "conditionally essential"). Different protein sources contain different ratios of amino acids, and are differently digestible. Some foods are quite low in certain essential amino acids, and so they don't work well as primary protein sources. People have come up with scoring systems (PDCAAS, DIAAS) to help judge how well different foods help you meet your protein requirements. Typically meats do very well, while plants do less well (though soy protein is decent, as is Quorn, which is made from mycoprotein), and dairy and eggs do the best. If you're vegan, however, you can typically combine multiple plant foods to end up with all the amino acids you need ("rice and beans" is a classic). It's important not to get all your protein from the same low quality sources (e.g. if you get almost all your protein from gluten-based foods like seitan, this is not great; even worse are sources made entirely from animal skin, like pork rinds). Protein source DIAAS (approximate; depends substantially on processing) Whole milk 1.43 Tofu 0.97 Cooked peas 0.82 Cooked rice 0.59 Almonds 0.4 Corn-based cereal 0.01 Source: Phillips (2017), "Current concepts and unresolved questions in dietary protein requirements and supplements in adults" (Frontiers in Nutrition) But protein quality isn't the only thing to pay attention to: It's also necessary to get a sufficient quantity of protein, so that your body has enough to build and maintain itself. Official guidelines here are around 0.8 grams per kilogram of body weight, but it's important to note that this is the amount needed to "prevent deficiency" in most people, i.e. to avoid becoming actively sick from missing amino acids. Two other facts are important to keep in mind about protein as you think about your diet: Of the macronutrients, protein typically has the greatest effect on satiety. So a calorie of protein will make you feel more full than a typical calorie of carbs or fat. How much protein you eat has a big effect on your body's tendency to build or lose muscle. If you eat more like 1.6-2.2g per kilogram of body weight per day, [5] this will allow your body to build muscle if paired with resistance training, or maintain your muscle and other lean tissues while losing body fat (instead of using those tissues for fuel as discussed above). So, overall takeaways: Humans need certain amino acids that we get from protein. Ideally people should get this protein from high-quality sources like animal protein or varied plant proteins, at around 0.8g/kg bodyweight in order to prevent disease, or 1.6-2.2g/kg in order to preserve or build muscle. Eating lots of protein is also good for keeping one's appetite in check. Fat Fats are a relatively complicated category of nutrient. They have in common that they are made partly of one or more "fatty acids", which are chains of carbon atoms flanked by hydrogen atoms. Dietary fats are typically classified based on the details of those fatty acids. The biggest distinction between types of fats is whether they're "saturated" or "unsaturated", which has to do with the structure of the fatty acid, and in particular whether it has any "extra space" for hydrogen atoms. You'll see this saturated/unsaturated distinction on the nutrition label. Structure of a saturated fat molecule (myristic acid) and an unsaturated fat molecule (oleic acid), respectively Generally, saturated fats are more common in animal-derived fats, while unsaturated fats are more common in plants. Diets with a lot of saturated fat have been associated with higher risk of cardiovascular issues (mostly higher LDL cholesterol; actual mortality risk is less clear, in that the judgement depends a lot on what you replace it with). Unsaturated fats are generally considered healthier, with a major exception: Structure of a trans fat molecule (elaidic acid) Trans fats are technically a kind of unsaturated fat. They are fairly rare in whole foods (though they do occur in small amounts in red meat and dairy), but are more common in processed foods. Trans fats are associated with increased cardiovascular disease risk. Fortunately in my country it has been much easier to avoid them since 2018: partially hydrogenated oils, which used to be the biggest source of trans fats, are now functionally banned in the US. There's a hypothesis that's fairly popular on social media that seed oils, which are mostly unsaturated fats, are actually really bad for you. I don't currently think this is supported by the available data; It seems more likely that it naively looks this way in observational studies, because seed oils are used in a lot of hyper-palatable processed foods that are bad for you, and that people overeat these foods. Another specific subcategory of fat worth mentioning is "omega-3 fatty acids", a specific type of unsaturated fatty acid, which you'd typically find a lot of in fish. Eating too little [6] omega-3 fatty acids is associated with heart issues, and a particular omega-3 fatty acid (EPA) may help with depression. Your body also needs two specific fatty acids from your diet: Alpha-linolenic acid is an omega-3 fatty acid (though one that comes from plants like flaxseed or walnuts instead of fish) that your body needs but can't make on its own. Linoleic acid is an omega-6 fatty acid that you also need in your diet (available in seeds and other plant oils). Takeaways: You need to eat a couple essential fatty acids that you will likely get from plant sources, and it's also good to get a moderate amount of omega-3 fatty acids from fish or algae. Unsaturated fats (but not trans fats) appear to be pretty healthy, while saturated fats may have negative cardiovascular effects (though this is still a bit disputed). Carbohydrates I have a bit less to say about carbohydrates than the other macronutrients. Some carbohydrates you can digest quickly and easily: they have a relatively large and fast effect on your blood sugar (glucose) levels, i.e. a high "glycemic index". Other carbohydrates are digested more slowly and have a more muted effect on blood sugar. Some carbs can't be broken down for energy at all, or only at very reduced efficiency: This is called "dietary fiber". You might think that dietary fiber has no purpose, since we mostly can't use it for energy. But in fact dietary fiber is very useful for your gut bacteria (it's sometimes called "prebiotic"), and certain kinds of fiber are associated with reduced cardiovascular disease risk ("soluble fiber", which is in fact broken down by some gut bacteria and does provide a small amount of energy, mostly in the form of fatty acids like butyrate). Fiber can also help with satiety: high-fiber foods will fill you up a lot faster per calorie than low-fiber foods. Your body can synthesize the relatively small amount of glucose it absolutely needs, so it’s not strictly necessary to get a lot of your energy intake from carbs, but eating more carbs will help your body keep larger stores of glycogen, which can substantially improve exercise performance. Ethanol Ethanol is pretty fun! But nutritionally it has some downsides. It's metabolized in your liver, where it is broken down into acetaldehyde (which is a carcinogen and harmful to the liver itself), before eventually being turned into acetate (which is not bad for you). It also gets metabolized before other macronutrients, so drinking ethanol can put a bit of a temporary brake on fat metabolism. Micronutrients Essential micronutrients are the things your body needs to eat that aren't macronutrients. They don't typically give you any energy, but they are important for performing various functions in your body, and your body can't make them (or can't make sufficient quantities) on its own. For each essential micronutrient there is some minimum amount a given person needs to eat to live, and in most cases there's also a maximum amount, above which you might experience negative effects (“toxicity”), sometimes just as serious as the negative effects of insufficiency. In some cases there's a wide range of acceptable intake amounts, while in other cases it's easy to end up with too much or too little. One thing that's important to note is that many micronutrients can be ingested in different forms (that is, a given micronutrient requirement can be fulfilled by multiple different molecules), and those different forms will not have the same recommended intake amount. Nutrition labels will typically normalize the amounts, so that you can get the right total amount given different forms. Vitamins Vitamins are the organic compounds that your body needs (but doesn't get energy from). They are identified with the letters A through E, plus K (and in some cases numbers). [7] Each of these letters actually refers to a collection of "vitamers", a set of different molecules with related functions. Functionally speaking choline is also a vitamin, though it doesn't get a letter (it was occasionally referred to as vitamin B4 in the past, but that label has been applied to multiple compounds so it's ambiguous). Essential minerals Essential minerals are specific chemical elements that your body needs, and they must be consumed in forms that your body can use (forms that are “bioavailable”). Intake works similarly to vitamins; the difference is chemical rather than practical (minerals are specific elements, while vitamins are organic compounds). Here comes a big reference table with the most important information about essential micronutrients! (Mini-glossary: RDA = Recommended Daily Allowance; AI = Adequate Intake; prev. = prevalence in the US) Nutrient RDA/AI (mg) M [1] RDA/AI (mg) F [1] Deficiency symptoms [2] Inad. Intake prev. [3] Deficiency prev. [4] Upper Limit (mg) [1] Toxicity symptoms [2] Vit A 0.9 0.7 Night blindness; dry eyes/skin; impaired immunity 51% <1% 3 Liver damage; bone loss; birth defects; headache Vit B1 (Thiamin) 1.2 1.1 Weakness; weight loss; cognitive issues; arrhythmia; swelling 7.2% Vit B2 (Riboflavin) 1.3 1.1 Cracked lips; sore throat; swollen tongue; dermatitis 2.4% Vit B3 (Niacin) 16 14 Dermatitis; dementia; diarrhea 2% 35 Flushing; liver toxicity; glucose intolerance Vit B5 (Pantothenic Acid)* 5 5 Fatigue; "burning feet" Diarrhea Vit B6 1.3 1.3 Anemia, dermatitis, confusion, seizures 15.1% 11% 100 Sensory neuropathy; photosensitivity Vit B7 (Biotin)* 0.03 0.03 Hair loss; dermatitis; neurological issues Distorts lab tests Vit B9 (Folate) 0.4 0.4 Megaloblastic anemia; birth defects; fatigue; neuro issues 12.8% <1% 1 Can mask B12 deficiency Vit B12 0.0024 0.0024 Megaloblastic anemia; fatigue; cognitive decline 3.9% 2% Vit C 90 75 Bleeding gums; poor healing; fatigue; corkscrew hairs 42.9% 6% 2000 GI upset; diarrhea; kidney stone risk Vit D 0.015 0.015 Rickets; soft bones; bone pain; weakness 95.4% 8% 0.1 Hypercalcemia; kidney stones; soft-tissue calcification Vit E 15 15 Nerve and coordination problems; hemolytic anemia 93.9% <1% 1000 Bleeding risk; interference with Vitamin K Vit K* 0.12 0.09 Impaired clotting; easy bruising; weak bones 71.1% Choline* 550 425 Fatty liver; muscle damage 91.7% 3500 Fishy body odor; low blood pressure; sweating Calcium 1000 1000 Osteoporosis; increased fracture risk 49.4% 2500 Kidney stones Chloride* 2300 2300 Metabolic alkalosis 3600 Tracks sodium excess Copper 0.9 0.9 Anemia; neutropenia; neuro signs 4.7% 10 GI distress; liver damage Iodine 0.15 0.15 Goiter; hypothyroidism; cognitive impairment 1.1 Thyroid dysfunction; goiter Iron 8 18 Anemia; fatigue; pica; brittle nails; restless legs 7.8% F:10%; M:<1% 45 Constipation; organ damage Magnesium 420 320 Cramps; tremor; arrhythmia; fatigue 60.9% 350 Diarrhea; arrhythmia Manganese* 2.3 1.8 11 Neurotoxicity Molybdenum 0.045 0.045 2 Gout-like (but rare) Phosphorus 700 700 Bone pain; weakness 1.8% 4000 Vascular calcification (in cases of kidney disease) Potassium* 3400 2600 Weakness, cramps, arrhythmia, raised blood pressure 97.6% Hyperkalemia: arrhythmia Selenium 0.055 0.055 Cardiomyopathy; impaired thyroid / immunity 1.1% 0.4 Hair/nail loss; garlic breath; neuropathy Sodium* 1500 1500 Nausea, headache, memory loss, fatigue, weakness, seizures High blood pressure; cardiovascular disease risk Zinc 11 8 Poor immunity and healing; hair loss; dermatitis; taste loss 11.9% 40 Copper deficiency; nausea; decreased HDL Key micronutrient data: fascinating! Notes: Most of the intake numbers here are "recommended daily allowances" while some (those with a *) are "adequate intakes"; the former are attempts to cover almost everyone's needs, while the latter is more like a guess based on observed patterns. Some of these intakes are in "equivalent units" that will match a nutrition label, rather than true mass. Source: National Academies of Sciences, Engineering, and Medicine. Dietary Reference Intakes for Sodium and Potassium, Appendix J: DRI Summary Tables (2019). https://www.nationalacademies.org/read/25353/chapter/28#569 These columns are the only content in this document that I've had an LLM (Claude Opus 4.8) generate. It claims the sources for this information are the Merck Manual, Professional Edition ("Overview of Vitamins" and "Overview of Minerals") and the NIH ODS Health Professional Fact Sheets; I’ve spot checked most of them against Wikipedia but not been extremely thorough. Source: Linus Pauling Institute Micronutrient Information Center, "Micronutrient Inadequacies in the US Population." https://lpi.oregonstate.edu/mic/micronutrient-inadequacies/overview#toc-micronutrient-deficiencies-and-inadequacies- Sources: CDC, Second National Report on Biochemical Indicators of Diet and Nutrition in the U.S. Population (2012) https://pmc.ncbi.nlm.nih.gov/articles/PMC4822995/ I think it’s especially interesting to look at the ratios between inadequate intake and clinical deficiency rates where you can see them. This might give you a very rough estimate of how serious it is to get less than the recommended intake - the deficiency numbers are about how many people display clinical signs of insufficiency, while the insufficient intake numbers are about how many people don't eat as much as they're recommended to. In some cases they’re very close together (Vitamin B6) while in others there’s a massive gap (Vitamin E). Similarly if you compare the RDA/AI with the upper limit (an amount that should not constitute too much of the nutrient for most people, if supplemented ), you’ll see big differences in how much leeway there is in dosing. A surprising fact is that magnesium's upper limit is lower than its RDA for adult men. I think this is down to that " if supplemented " caveat: the numbers are saying that you need 420mg/day of magnesium from all sources, and less than 350mg of that ought to come from supplements. Other nutrients There are many other things we consume that are not (or not always) considered “essential nutrients”. Water An extremely important nutrient we haven’t talked about is water: It’s very possible to die due to not consuming enough water and/or losing too much water via diarrhea or sweat; unfortunately the literature is very unclear on exactly how much water is essential for an individual: it varies a lot from person to person and day to day, and “enough to not die” is going to be way less than the optimal amount of water. As with other nutrients, it is also possible to consume too much water, and people have died that way. All that said, among healthy people in Western countries it’s very rare to die due to either dehydration or water intoxication. Your personal optimum water intake is probably relatively close to, or slightly above, the amount of water you feel inclined to drink. Supplements There are thousands of recommendations for supplements and peptides and so on, some of which you’ll see in the pharmacy aisle. Most of the online discourse around this stuff doesn’t pass the “strong sniff test” bar I’m using for this document, so I’m going to add on just one more thing that does seem to me to be worth at least clearly looking at, out of the thousands out there: Creatine. Supplementing creatine is helpful for strength and athletic performance in most people, and has even been linked to positive psychological effects. One important note is that creatine can make kidney lab results look superficially worse than they should, because creatine can result in elevated creatinine levels, which would normally be a sign of decreased kidney function. So it’s important to let your doctor know about creatine supplementation when you get metabolic tests. Exercise There are two relevant things that happen in your body when you exercise: You expend energy, and you provide signals to your tissues that cause them to change. Energy expenditure We discussed energy intake above. The other side of the equation is energy expenditure . Basal Metabolic Rate Your body has what’s called a “basal metabolic rate” (BMR), which is the amount of energy you expend when doing “nothing”: If you were in a coma, you’d still spend a lot of energy just to keep all your cells and organs running. There are formulas that estimate how much energy this is. If you know your body fat percentage, you’d want to use the Katch-McArdle formula: First calculate your lean body mass (LBM) by multiplying your weight in kg by (1 - body fat percentage / 100). Then your BMR in kcal = 370 + 21.6 * LBM in kg. If you don’t know your body fat percentage, you can use a different formula called the Mifflin-St Jeor equation to get an estimate: Men: BMR in kcal = (10 * weight in kg) + (6.25 * height in cm) - (5 * age in years) + 5 Women: BMR in kcal = (10 * weight in kg) + (6.25 * height in cm) - (5 * age in years) - 161 These formulas will give you an estimate, but people can have BMRs that differ a lot from the formula outputs. Your BMR is also not a fixed number, but adapts to factors like your diet and exercise level. Total Daily Energy Expenditure Your body will also spend energy on other things: sitting, standing, fidgeting, walking around, and exercising will add energy expenditure to your BMR. You also burn some calories on the “thermic effect of food”, i.e. digestion, depending on what you eat. The amount of energy you actually expend in a day is called your Total Daily Energy Expenditure (TDEE). This is the number you need to balance against your energy intake in order to lose, maintain, or gain weight. [8] It might be surprising that, for most people (even quite active people), most energy expenditure actually goes toward BMR rather than exercise. For example, my current estimated BMR is around 1900kcal/day, and my TDEE is only about 700kcal higher, at around 2600kcal/day. Doing exercise does increase your TDEE, and thus can help you burn fat. But in terms of marginal effort, for most people it’s easier to persistently restrict energy intake (i.e. eat, say 100kcal less per day) than it is to persistently increase energy expenditure (i.e. do an extra 100kcal of running per day). Resistance training Resistance training is exercise that requires relatively large amounts of force, like lifting weights. Resistance training is mostly done to get stronger and to increase muscle mass, both of which have lots of downstream positive effects (including increased TDEE and better insulin sensitivity, not to mention benefits for attractiveness. Daniel Filan points out: "Also, perhaps crucially, you're more able to move around in the world and carry + manipulate heavy objects!"). When you exercise, this puts some parts of your body under stress, and they adapt to accommodate that pattern of exercise better: your nervous system will become more coordinated and effective in achieving that movement, and various tissues will adapt to better supply resources to the stressed tissues. In the case of resistance training, the muscles you use for that exercise will get bigger and stronger. This is really cool, but it also means your progress will eventually stall if you keep doing exactly the same exercises at the same intensities. So if your goal is to get stronger, increase muscle mass, or preserve muscle while losing weight, the way to predictably accomplish that in the long run is to employ some form of progressive overload : Increasing the total stimulus (i.e. the force and the amount of stressed time) you’re applying to a given muscle in each workout, so that your body can’t “rest on its laurels”. If you did three sets of 10 repetitions with 30lbs of weight last workout, this workout, you might try doing three sets of 11 reps of 30lbs, or three sets of 10 reps with 35lbs this workout. You won’t always succeed in increasing the difficulty every workout, but if you’re healthy and eating enough (especially enough protein), over the long run you should be able to get stronger and your muscles should grow. If you’re in a substantial energy deficit, you may not be able to build muscle, but at least you should be able to prevent muscle loss , which would otherwise happen during phases of substantial weight loss. Building muscle is a very common concrete fitness and health goal, and there exists a fairly strong mechanistic “if you do this, then that will happen” understanding that applies to most people. With that in mind I’m going to break a bit from the otherwise non-normative frame of this document to share some standard recommendations among exercise scientists and people focusing on resistance training: To maximize muscle growth (“hypertrophy”) you should aim for your sets to end 0-3 reps away from failure (i.e. at most 3 “Reps In Reserve” or RIR). To see progress and avoid injury, choose the weight so that this 0-3 RIR target lies somewhere in the range of 5-30 repetitions. This will take some trial and error at first, and you should try to take at least some sets all the way to failure (i.e., you should not be able to complete the last rep you attempt), to ensure you really are getting close with your other sets. To maximize endurance, aim for the higher end of reps in that range (more like 25-30), and to maximize single-rep strength, aim for the lower end of that range (more like 5-8). Any amount of resistance training is better than none. Indeed, as you increase the number of sets per week, each additional set is slightly less valuable than the last (there are “diminishing marginal returns”). Typically, serious lifters will aim for around 12 sets per week per muscle group, but beginners should see noticeable gains with as few as 3 sets per week. It is allegedly quite important for the effectiveness of resistance training to get sufficient high-quality sleep. For the most part, especially for beginners, the more controlled your movements, the better: If you let your arm lower the weight by totally relaxing rather than effortfully lowering it over a second or two, you’re missing out on some of the gains you’d get from that rep; and if you use a lot of momentum when lifting you increase your injury risk. Don’t push through joint pain if you notice it persistently in the same spot during a certain lift, as this can be a warning sign for injury. Instead, try variants of the exercise, or change your target number of reps (lighter weight for more reps can be safer) Aerobic exercise / cardio When you think of exercise, you probably think first about aerobic exercise: walking, cycling, swimming, running, and so on. This kind of exercise can burn a lot of calories, improves your cardiovascular health, and helps you live longer. Unfortunately, I haven’t yet managed to build solid-feeling models, so I both (a) don’t have very much I want to say about it here, and (b) haven’t managed to incorporate it into my life in a way that’s satisfying. Basically I think aerobic exercise is in fact extremely good for you, but I don’t have a strong sense of exactly what kinds of aerobic exercise are best for you, per unit of effort. I’m not claiming that the literature doesn’t have clear answers here; merely that I don’t know what they are (though I have tried a bit, and my impression is that the story of what works well for cardiovascular health is more complicated and has less overall consensus than what works well for skeletal muscle). Summary + What I personally do with these models So, to wrap all this up: tl;dr Energy balance (intake - TDEE) is the most important thing to pay attention to for weight and body composition, followed by protein intake and resistance training. There are certain recommended minimum intakes for macronutrients and micronutrients (see the relevant tables). In resistance training, progressive overload leads to muscle and strength gains; cardio is good for you but I don’t (yet) have enough details resolved to tell you much more than that. What’s been working for me I can’t stop myself from telling you what I’m personally doing, downstream of these models. Over the last year I’ve lost over 50lbs of almost pure fat (~20% of my body weight 10mo ago) according to DEXA scans. These are things I’m doing, ordered by how important they feel to me. I log my food . I’m especially careful to estimate my calories and my protein intake. I’ve done this every day for the last six months, and one month I also tried to carefully log my micronutrient intake to get a sense of what I might not be eating in adequate quantities by default. I've been using MacroFactor for this and logging weight; any similar tool or even just a spreadsheet would work, but MacroFactor has nice colors and feels sort of gamified in a helpful way. I weigh myself every morning and pay attention to a running average of my weight. I aim fairly religiously to eat at least 1.1g of protein per lb of lean body mass, per day, plus at least 20g of fiber . This makes it much easier to stay in a caloric deficit. I aim to lose, on average, about 1.5lbs per week (which comes to a deficit of around 750kcal per day) My body seems to do staircase-style weight loss, where it will look like nothing is happening for a week and then I’ll wake up one morning down 5lbs or more. I put a bunch of weight lifting equipment in my bedroom (adjustable dumbbells, a weight bench, and even a mini lat pulldown machine). This minimizes the activation energy for me to do resistance training, and it’s let me get around a general dislike of working out where people can see me (especially when I was much fatter, this was a big problem for me). I do resistance training at least 4 days per week (aiming for progressive overload on chest press, lat pulldowns, and curls, plus some maintenance sets of dumbbell squats). I only technically force myself to do 1 total set per workout across all lifts, but in practice I typically do 5-10. I aim to do about 12k steps per day, spread across intensity levels (though I don’t hit this target every day). I get regular DEXA scans to ground my body fat and lean mass numbers. After the month of logging my micronutrients carefully, I started taking some supplements to make sure I’m hitting the minimum amounts for various vitamins and minerals . The nutrients I’m most confident I should supplement given my diet are (in order): Vitamin K, Magnesium, Omega 3s, and Vitamin D. I actually ended up designing a custom multivitamin based on the data I collected, and ordering it from a Canadian company that lets you specify the nutrients you want in your vitamin. I want to highlight that this specific action is especially not advice; it’s expensive, probably overkill, and I think most doctors would recommend trying to make sure your diet covers your micronutrient needs, rather than supplementing. But personally I have found it quite hard in practice to change my diet in this way while also meeting all the macronutrient constraints. I should note that earlier in the year I was prescribed tirzepatide, which I took for a little over a month, but stopped partly due to annoying side effects (similar to side effects that had earlier stopped me from taking semaglutide). It was helping me, especially with appetite, and I think it’s awesome that we’re finally getting drugs that really can help people in this domain. But eating a lot of protein and fiber seems to be enough that I haven’t actually needed this kind of drug during most of my weight loss. That’s it! I hope some of this is helpful to someone; let me know if you notice any inaccuracies or want more information. ^ There’s unfortunately barely anything about aerobic exercise, since I’ve found it much harder to build a solid model of the critical information about that. ^ I've tried to stick to claims that I think are durable consensus views in nutrition science, and to mention where things are more speculative. I learned most of this material over several years, mostly from people on YouTube. I wasn't planning to write it up, so I don't know exactly where I learned what, and I haven’t gone to the trouble of finding citations for most things. None of the text is LLM-written, but I've asked GPT-5.5 and Claude 4.8 Opus to find errors (and clarified a few things they objected to), and in most cases I've checked claims against Wikipedia. I haven't read almost any of the actual underlying research. Here's a partial list of YouTube channels and blogs where I learned this stuff: * General high-quality blogs that sometimes touch on relevant health topics: * https://dynomight.net * https://blog.ncase.me * https://www.astralcodexten.com * YouTubers focusing on weight lifting (bodybuilding, strength training) * https://www.youtube.com/@menno.henselmans * https://www.youtube.com/@JeffNippard * https://www.youtube.com/@RenaissancePeriodization * YouTubers focusing on general health, which in many cases ends up looking like a lot of videos about supplements: * https://www.youtube.com/physionic * https://www.youtube.com/@DrBradStanfield * https://www.youtube.com/@DoctorMike The sources above seem to me to be generically high-quality information. I've also found the sources below useful, though I think they are more likely to overreach about implications, and to sometimes either be out of date, or make claims that aren't actually clearly supported by the evidence. In particular, they're prone to repeating "conventional doctor-isms" even in cases where those doctor-isms have been refuted. This strikes me as typically less dangerous than the standard social media influencer making wild claims, because doctor-isms are at least (a) believable by doctors, and (b) sufficiently harmless that doctors basically never get sued for saying them. Still, I think it's worth being a bit more skeptical of these. * https://www.youtube.com/@theanatomylab * https://www.youtube.com/@DrAlexWibberley There are also a ton of other fitness influencers (including some doctors) who I think have much lower standards for claims they make than those listed above. Andrew Huberman, Tim Ferriss, Bryan Johnson, and many others could be worth watching for entertainment or interesting hypotheses, but they’re typically happy to state things more strongly than one ought to infer from the available information. ^ A note about units: Confusingly, a kilocalorie and a capital-c Calorie are the same unit. I'll usually abbreviate it as "kcal" ^ This is more energy per gram than energy stored as fat, because when your body stores energy as adipose tissue, that tissue also includes other components (e.g. water) that go away as the fat is used. ^ If you’re obese you may want to instead aim for 2g per kg of lean mass , i.e. subtract your estimated body fat weight from your weight, then multiply by 2g to get a daily intake recommendation) ^ or, less confidently, supplementing too much ^ Vitamin names have a somewhat complicated history. There are gaps in the sequence where people incorrectly assigned certain chemicals vitamin status; and in the case of some vitamins (especially B vitamins) they slowly learned that a certain “vitamin” was actually several different compounds with different roles. ^ Energy expenditure that’s neither “basal” nor a part of a “structured exercise program” is referred to as Non-Exercise Activity Thermogenesis, or NEAT. I have avoided talking about it here because I don’t think it’s a very useful categorization for average people. There’s no real difference between deciding to walk to work to burn calories, and taking the same walk as part of a “structured exercise program”, but NEAT includes one and not the other. This seems to me like an unfortunate distraction, especially since people often imprecisely use NEAT to refer to specifically involuntary movements, changes in which can have surprisingly large effects on energy expenditure. But then on the other hand there is a lot of official advice about increasing your NEAT, which of course is not possible to do when focusing on involuntary movement. It strikes me as a big mess. Discuss