Functional, sustainable nutrition habits are critical for living a healthy life. You can’t exercise enough to make up for eating poorly1 so, at the very least, you must eat well enough for a solid foundation. The key characteristics of a good diet are:

  1. It keeps you in the right energy balance to achieve your goals.
  2. It provides enough protein to help you build muscle.
  3. It promotes metabolic health by avoiding spikes in blood sugar and the subsequent insulin response.
  4. It is enjoyable enough that you can maintain adherence over time.


Science can provide the foundation for functional nutrition and the framework to make deliberate modifications. However, just as it is in training, your nutritional needs are unique to you, the activities you engage in, and your life situation. You will need to experiment, observe, and make refinements to determine what works best for you.

The information compiled here attempts to distill practical applications of nutritional science. However, it can be easy to get lost in the weeds, chasing down details that aren’t important, if science is your only tool. The opening of Mastering Mindful Eating by Michelle Babb contrasts the “art” of eating with the science of nutrition. The art of eating embraces the experience of eating and listening to your body; practices like this are a reminder to invest in your holistic health. Don’t just optimize metrics; live your life.

Energy Balance

Energy balance is the relationship between the amount of energy your body needs and the amount of food you eat each day on average.

The amount of energy your body burns each day depends on your activity level, your genetics, your gut microbiome, and a host of other factors. It’s difficult and unreliable to guess your energy needs and you should not put any stock in any estimated “exercise calories” numbers generated by fitness trackers or gym equipment.

The only way to get an accurate idea of what your energy needs are (outside of a stint in a metabolic ward) is to carefully and precisely track all of the things you eat (use a scale!) and record your weight over time.3 Once you know your total daily energy expenditure (TDEE) and your desired state of energy balance you can determine your daily calorie target. Your caloric budget can then be divided into target amounts for the three macronutrients.


There are three dietary macronutrients (called “macros” colloquially):

Carbohydrates and fats are used as fuel or stored for later. Protein is used to build, repair, and replace tissues, cells, and cellular structures.


Carbohydrates are a class of nutrients that are similar in chemical structure but vary in complexity. Sugars are the simplest and are digested the fastest. Starch is the most complex and must be broken down into sugars before it can be further digested.

Carbohydrates are a critical part of a functional diet. Do not avoid eating them to be “healthy.” Consumption of refined carbohydrates like white flour and added sugar can impact your metabolic health and should be done in moderation. Favor longer-digesting, lower glycemic index sources of carbohydrates like whole grains (it’s best if they’re not ground into flour), legumes (beans, lentils peanuts), sweet potatoes, cruciferous vegetables, and others too numerous to list here. Eating carbohydrates in combination with fat, protein, and fiber helps regulate their digestion and absorption.

The common dietary sugars are glucose and fructose. Table sugar is about a 50/50 mix of glucose and fructose while high-fructose corn syrup is 60% fructose and 40% glucose. Glucose and fructose are metabolized in different ways.

The liver uses carbohydrates to create and store glycogen which your body uses to maintain glucose homeostasis during long bouts of exercise. Endurance athletes “bonk” when they run out of glycogen and the nutrients they’re absorbing from the food they’re eating during the activity can’t keep up with their energy (and/or electrolyte) needs.


You can vary the distribution of carbohydrates and fat in your diet to meet your energy needs but your body requires a certain amount of protein intake to maintain muscle mass and even more to promote increasing muscle mass. Since growing your muscles is critical for your long-term health, you must pay attention to your protein intake. To do this, you must consider:

The main takeaway here is that you need to eat a lot of protein to support growing and maintaining muscle—almost assuredly more than you would eat without being deliberate about it.7


Fat is an essential nutrient. Your body requires enough dietary fat to support a healthy endocrine system as fat is an essential ingredient for hormone production. Dietary fat intake can also impact many areas of brain function; it is necessary for cognitive health.

Most people eat too much total fat while simultaneously not eating enough of specific kinds of fat.

Your body preferentially uses carbohydrates as fuel. Fats are left in reserve unless you sustain a negative energy balance over time or eat so few carbohydrates you enter and maintain ketosis. Using fat as your primary fuel can be helpful in specific situations:

Ketogenic (“keto”) diets aren’t a great idea in the long term.

Physique athletes, like bodybuilders, must maintain a very low fat intake to get to competitive levels of leanness. This can cause all kinds of issues as you’re depriving your body of an essential nutrient. There may not be any long-term consequences for doing this occasionally but you can’t maintain extremely low levels of body fat and have good long-term health outcomes.


Macros aren’t everything. Your body needs lots of different vitamins and minerals in trace amounts. It’s tempting to use supplements to meet these needs but it’s better to get micronutrients from real, minimally processed food if you can.

The supplement industry is loosely regulated and rife with bold claims that are hard to verify. Ask yourself these questions before taking a supplement:

You will probably benefit from some supplementation depending on your training needs. is a good place to start your research. However, figuring out which supplements and how much to take for your specific situation can be tricky to figure out on your own. Talk to a nutritionist—ideally with credentials in sports nutrition—if you can.


Dietary fiber helps digestive health and, in general, is a good proxy for seeing if you’re eating enough minimally processed fruits and vegetables. The RDA for fiber (28g per 2000 calories) is almost assuredly more than you are eating now unless you’re being deliberate about it.

The fiber in your diet that comes from food helps regulate nutrient and sugar absorption in addition to being good for your GI health. Fiber supplements, in pills or added to processed food, don’t do the same thing.

Metabolic Health

Metabolically healthy people can switch between using glycolytic (glucose-based) energy sources and fatty-acid-based energy sources. Metabolic health is underpinned by mitochondrial function. Mitochondrial function is improved by endurance training and, unless you are currently doing several hours of endurance training a week, you are almost certainly not metabolically healthy.

Metabolic health is also influenced by diet. Specifically, spikes in blood glucose—and the corresponding spikes in insulin response—can be moderated with dietary factors:

The factors listed above all point to the benefits of moderation. Tempering the amount and the speed at which sugar enters your bloodstream helps your body maintain glucose homeostasis without having to work too hard. Keep your pancreas and your liver happy; they’ll thank you for it later in life.

Your blood sugar levels are a good proxy for understanding your metabolic health. The most accurate way to track your blood glucose is with a continuous glucose monitor (CGM) like the ones made by Dexcom.10 Because they can be used to administer insulin as medical devices, CGMs aren’t readily available to consumers unless you have a prescription from your doctor.

Palatability & Pleasure

Eating good food is one of life’s simple pleasures. If you don’t enjoy what you’re eating enough then you cannot to sustain your eating habits for the long term. The trick is finding the right balance between:

The most important thing is to find the food you like to eat that meets your nutritional needs. Changing your diet can change your palate11; what you like in the future may not be the same things you crave now. And, even when you’re eating the kind of food you need consistently, it’s still a good idea to have the occasional meal or, or day, where you eat whatever makes you happy.12

  1. People who do hours a day of endurance training can eat a lot and get away with it. Even so, it is always possible to outpace your calories burned by over-eating. 

  2. The “constrained energy model” explains this phenomenon. It posits that your body can compensate for changes in energy needs by raising and lowering several metabolic and hormonal processes. This change is helpful if you’re living with food scarcity but works against you if you’re living with an abundance of food and trying to “burn off” the rest with exercise. 

  3. This method is exactly how MacroFactor works. I have had a great experience using that app to lose and maintain weight. 

  4. There are technically three types of carbohydrates classified by their degree of polymerization. From smallest to largest molecule size they are sugars, oligosaccharides (like maltodextrin), and polysaccharides (starch is not the only polysaccharide). Most people don’t need to know about this. 

  5. We believe the mutation introduced the metabolic pathway that preferentially turns fructose into fat happened when early humans were desperate to survive the last ice age. It kept us alive when food was scarce. It’s killing us now in times of plenty. 

  6. mTOR (Mammalian target of rapamycin) is the primary signaling mechanism for muscle protein synthesis. 

  7. The daily Recommended Dietary Allowance (RDA) for protein, while enough to keep you alive, is only a half to a third as much protein as it takes to maximize muscle protein synthesis. 

  8. Salmon from fish farms does not have the health benefits of wild-caught salmon. Farmed fish don’t eat the same diet as wild fish. They have much lower concentrations of omega-3 and omega-6 fatty acids. However, depending on the farming facility, they may have lower mercury levels than wild-caught fish. 

  9. An early advocate of MCT-oil-to-start-the-day was bulletproof coffee. Dave Asprey, who founded Bulletproof, has been peddling fringe (*cough* “innovative”) health ideas since before 2011 so take it with a grain of salt. In my experience, as little as a half tablespoon of MCT oil in a cup of black decaf coffee first thing in the morning has a perceptible benefit without any GI consequences. 

  10. There is a clear benefit for CGM devices in people with diabetes and those who are at risk of developing diabetes. The benefit for metabolically healthy people is less clear. They are still a window into what is happening in your body. 

  11. I followed a ketogenic diet for over a year. In that time, my sugar cravings essentially disappeared. My mood also improved. 

  12. If you have diabetes don’t be careless; you could die. As long as you are metabolically healthy, you can take some form of “diet break” for a week or two, like on a vacation or the holiday season, and the consequences won’t be too dire—especially if you maintain reasonable portion sizes.