Functional, sustainable nutrition habits are critical for
living a healthy life. You can't exercise enough to make up
for eating poorly[^1] 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_](#energy-balance) to achieve your goals.
2. It provides [_enough protein_](#protein) to help you build muscle.
3. It promotes [_metabolic health_][1] by avoiding spikes in blood sugar and the subsequent insulin response.
4. It is [_enjoyable enough_](#palatability--pleasure) that you can maintain adherence over time.

## Mindset

Science can provide the foundation for functional nutrition
and the framework to make deliberate modifications. However,
just as it is in [training][1], 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_](https://www.penguinrandomhouse.com/books/624254/mastering-mindful-eating-by-michelle-babb-ms-rd-cd/)
by [Michelle Babb][2] 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_.

- A _positive energy balance_ means you are eating _more_ than you need.
    - It is easier to build muscle in a positive energy balance.
    - Your body stores excess energy in adipose tissue (fat) when you maintain a positive energy balance.
- A _neutral energy balance_ means you are only eating enough to _maintain_ your current body weight.
	- You do not need to adhere to a precise number of calories per day to be in a neutral energy balance. Your body has about 400–600 calories of "wiggle room" on a daily basis.[^2]
- A _negative energy balance_ means you are eating _less_ than you need.
    - Muscles waste away faster in a negative energy balance.
	    - You can limit the disproportionate loss of muscle mass by maintaining a deficit at or below 400 calories per day.
    - Your body _uses up_ the excess energy stored in adipose tissue when you maintain a negative energy balance.

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.

## Macronutrients

There are three dietary macronutrients (called "macros"
colloquially):

- _Carbohydrates_ are sugars and starches.[^4]
    - Carbohydrates are the primary source of fuel for your body.
    - When you are in positive energy balance, and especially if you are in poor [metabolic health][3], your body uses carbohydrates as fuel almost exclusively.
- _Protein_ is made up of amino acids; it is primarily used to build the proteins your body needs.
    - Protein _can_ be used as fuel but it isn't very efficient; your body favors other sources of energy.
    - Protein deserves special attention for its role in building and maintaining muscle.
- _Fat_ is made up of fatty acids and, in [metabolically healthy people][3], it can be used as fuel—especially when you're in a negative energy balance.
    - Dietary fat is easy for your body to store as adipose tissue if you are in a positive energy balance.

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

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][3] and should be done in
moderation. Favor longer-digesting, lower [glycemic
index][4] sources of carbohydrates like whole grains (it's
best if they're not ground into flour), legumes (beans,
lentils peanuts), sweet potatoes, [cruciferous
vegetables][5], and others [too numerous to list here][6].
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 pure sucrose, a disaccharide, which breaks down
into a 50/50 mix of glucose and fructose, both
monosaccharides, during digestion. In contrast,
high-fructose corn syrup is either [42% or 55% fructose][7].
Glucose and fructose are metabolized through different
pathways in your GI tract.[^5]

- If you're trying to maximize carbohydrate intake—like during an endurance race that lasts longer than 45 minutes—consume a balance of glucose and fructose.
	- Fructose metabolism is different between men and women. [Dr. Stacy Sims recommends][8] that women _avoid_ fructose as an endurance fuel because a consuming a large bolas of fructose can induce GI distress. She favors maple syrup [which is principally sucrose][9]—and thus requires digestion to split it into glucose and fructose, slowing the release of fructose into your gut.
- Fructose is preferentially turned into adipose tissue.[^6]

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.

### Protein

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][10] is critical for your long-term
health, you _must_ pay attention to your protein intake. To
do this, you must consider:

- The total amount of protein you eat.
    - Your body turns over [300–400g of protein per day][11] through normal metabolic processes.
        - Your body can get up to 50% of the protein it needs by recycling amino acids from the protein that has broken down.
        - As you age, the rate you can successfully recycle protein goes down. Because of this, you need a corresponding _increase_ in dietary protein to avoid being in a protein deficit. This decline isn't linear; there is a sharp drop off after age 40.
    - A daily target of [1.2–1.8 g/kg/day of dietary protein][12] maximizes muscle protein synthesis.[^7]
        - The [RDA for protein][13] is .8 g/kg/day. This is too low to support [training][14] and [muscle growth][10].
        - 1.4–1.8 g/kg/day is ideal. Above 1.4 g/kg/day the quality of the protein you eat matters less.
        - Some fitness influencers advocate for 1g/lb/day of high-quality protein (2.2 g/kg/day). This is way more than you need.
    - A serving of protein that you're digesting is called a bolus.
        - The _minimum_ effective size of a bolus is around 25g; smaller servings don't activate mTOR.[^8]
        - The _maximum_ effective size of a bolus is around 60g; any more is discarded as waste.
        - You should split your protein consumption into 3–4 different feedings for best absorption.
- The "[quality][15]" of the protein you eat.
    - The three most important amino acids for muscle protein synthesis are leucine, lysine, and methionine.
        - Leucine in particular is critical; aim for ≥3g of leucine in the first and last meals of the day (this usually requires about 45g of protein but the exact amount depends on the amino acid distribution of what you're eating).
        - FUN FACT: Leucine is ketogenic; it is metabolized as a fatty acid because of its structure.
    - The quality of the protein you eat matters less the more protein you eat.

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.[^9]

### Fat

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.

- Polyunsaturated fats, including omega-3 and omega-6 fatty acids, have clear long-term health benefits when consumed regularly in sufficient quantity. Good sources of polyunsaturated fat include sunflower seeds, flax seeds (and oil), algae oil, and wild-caught[^10] fatty fish like salmon, herring, mackerel, etc. Most people don't get enough in their diet without supplementation or deliberate planning.
- Saturated fat should be eaten in moderation as it contributes to the risk of atherosclerotic cardiovascular disease (ASCVD).
- Artificially created trans-unsaturated fatty acids (trans fats) are _very bad_ for ASCVD. Avoid partially hydrogenated oil and other sources of trans fat in your diet.
- Dietary cholesterol is almost exclusively _esterified_ cholesterol. Esterified cholesterol molecules are too large to be absorbed in your digestive system; they are just excreted. _Dietary cholesterol has NO IMPACT on blood cholesterol._
- Medium-chain fatty acids, like MCT oil, can be easily metabolized into ketones which your brain can use as fuel. They can give you a bit of a mental boost in your morning coffee.[^11]

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][16]. Using fat as your primary fuel can
be helpful in specific situations:

- For endurance athletes in extremely-long-duration events.
- As an augmentation to a cancer treatment plan for cancer patients; cancer cells can multiply at a prodigious rate because they can metabolize up to 500 times more glucose than a normal cell. Starve them and it gives other therapies a competitive advantage.
- As part of a targeted, short-term fat-loss program.

Ketogenic ("keto") diets aren't a great idea in the long
term.

- It is easy to have a high saturated fat intake which, as noted above, is bad for the long term health outcomes.
- They forbid many kinds of food and require a lot of food prep so they are prone to diet fatigue.
- Things go off the rails easily. If you eat enough carbs to get _out_ of ketosis _while_ eating a lot of fat it's not a good situation.
- Your liver is responsible for producing the ketones your body needs as fuel while in ketosis. Drinking alcohol can compromise its ability to do that.
- In general, it's not a good idea to eliminate one of the three macronutrients from your diet.

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.

## Micronutrients

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:

- Are you getting a large enough dose for it to have a meaningful effect?
- How does the bioavailability of the _form_ or the micronutrient in the supplement compare to food sources?
- Do you need additional nutrients to effectively process it?
- How consistent is the supplement potency from batch to batch?
- High-quality supplements are _expensive_. Are they worth the cost to you for the benefit they provide?

You will probably benefit from _some_ supplementation
depending on your training needs. [Examine.com][17] 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.

## Fiber

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][18] 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 total amount of carbohydrates in your diet.
    - One rule of thumb is to keep carbohydrates to less than 30g/meal to dampen insulin response.
- The [glycemic index][4] of the carbohydrates you consume. The higher the glycemic index the faster sugar enters your bloodstream.
    - Carbohydrates in unprocessed foods, like vegetables, are stored in and around dietary fiber which slows their digestion.
    - Processed, and especially hyper-processed, foods digest _faster_ which causes spikes in blood sugar.
- Energy balance also plays a role in metabolic health.
	- Maintaining a negative energy balance can adversely affect your metabolic health because your body reacts to the calorie deficit by slowing your metabolism.
	- Maintaining a positive energy balance means your body is far more likely to _only_ use glycolytic energy sources for fuel; this effect is more pronounced the larger the energy surplus. Many diabetic and pre-diabetic people have lost the ability to use fatty acids as fuel and thus _depend solely_ on energy from the sugar that's wreaking havoc on their overall health.

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][19].[^12] 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:

- Meeting your nutritional needs
- Exercising enough
- Having times when you can enjoy yourself

The most important thing is to find the food you _like_ to
eat that meets your nutritional needs. Changing your diet
can change your palate[^13]; 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.[^14]

[^1]: People who do hours a day of [endurance training][16] _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][20]" 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][21] 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]: There are different intestinal transporters to handle these monosaccharides: SGLT1 for glucose, GLUT5 for fructose.
[^7]: [Eric Trexler, Ph.D.][22] pointed out that looking at the data points in [Figure 5][23] in [Morton et al. 2018 (PMID 28698222)][12] there is a linear regression that tracks back to 1.2g/kg/day, slightly lower than the 1.4 g/kg/day floor suggested by the authors.
[^8]: [mTOR][24] (Mammalian target of [rapamycin][25]) is the primary signaling mechanism for muscle protein synthesis.
[^9]: The daily [Recommended Dietary Allowance (RDA) for protein][13], while enough to keep you alive, is only a half to a third as much protein as it takes to maximize muscle protein synthesis.
[^10]: 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.
[^11]: An early advocate of MCT-oil-to-start-the-day was [bulletproof coffee][26]. 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.
[^12]: 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.
[^13]: I followed a ketogenic diet for over a year. In that time, my sugar cravings essentially disappeared. My mood also improved.
[^14]: _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.

[1]: /health/training/#personalize-your-training
[2]: https://eatplaybe.com/books/
[3]: #metabolic-health
[4]: https://en.wikipedia.org/wiki/Glycemic_index
[5]: https://en.wikipedia.org/wiki/Cruciferous_vegetables
[6]: https://www.sciencedirect.com/science/article/pii/S0002916523058409?via=ihub
[7]: https://www.fda.gov/food/food-additives-petitions/high-fructose-corn-syrup-questions-and-answers
[8]: https://www.drstacysims.com/roar
[9]: https://mapleresearch.org/wp-content/uploads/1206sugarprofilessyrupgrades.pdf
[10]: /health/strength-training/
[11]: https://pubmed.ncbi.nlm.nih.gov/22139560/
[12]: https://pubmed.ncbi.nlm.nih.gov/28698222/
[13]: https://www.ncbi.nlm.nih.gov/books/NBK56068/table/summarytables.t4/?report=objectonly
[14]: /health/training/
[15]: https://en.wikipedia.org/wiki/Protein_quality
[16]: https://en.wikipedia.org/wiki/Ketosis
[17]: https://examine.com
[18]: /health/endurance-training/
[19]: https://www.dexcom.com/en-us
[20]: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4803033/#:~:text=In%20Constrained%20total%20energy%20expenditure,expenditure%20within%20a%20narrow%20range.
[21]: https://macrofactorapp.com
[22]: https://scholars.duke.edu/person/eric.trexler
[23]: https://pmc.ncbi.nlm.nih.gov/articles/PMC5867436/figure/F5/
[24]: https://en.wikipedia.org/wiki/MTOR
[25]: https://en.wikipedia.org/wiki/Sirolimus
[26]: https://www.bulletproof.com/recipes/bulletproof-diet-recipes/bulletproof-coffee-recipe/