Formed in the Depths

Calories and Macro Basics

"Calories" or kilocalories/kcal are a unit of energy. 1 kcal is the energy it takes to raise the temperature of 1 L of water by 1 degree C.

A body's Basal Metabolic Rate (BMR) is how many calories it burns simply existing and living, also called "coma calories" because it does not include any movement whatsoever. Additional calories are included in Total Daily Energy Expenditure (TDEE) by one's daily activities.

There are 3 macronutrients: carbohydrates, proteins, and fats. Carbs and proteins each contain 4 kcal/g, and fats contain 9 kcal/g. The basic building blocks of carbs are sugars, of proteins are amino acids, and of fats are fatty acids. The body can break these down and rearrange them, but there are limits. All three have their places and uses.

When food is consumed, the body extracts caloric energy from macronutrients, and that's the basis of digestion and metabolism, cellular respiration. The energy released from these molecules fuels physiologic reactions. If energy in/kcal consumed = energy out/TDEE, that's eating at maintenance.

When we consume more energy than is needed to maintain our physiology (calorie surplus), the body usually stores this excess energy as fatty acids within adipocytes. It does this when it can because fat is the most calorically dense of the macros, making for efficient storage. However, if a person is strength training to build muscle, the muscle cells will take in that energy and available amino acids to build their structural proteins and grow. Whatever they don't use then goes to fat. It doesn't matter very much which macro is dominant in a diet: if there is a calorie surplus, those calories are getting stored. Nuance is just that muscles can only grow if they have enough amino acids available to synthesize their proteins -- you can't really build muscle out of carbs and fats. When we consume less than is needed (calorie deficit), the body draws from those energy stores to power reactions, burning fat.

Moderate, sustainable weight loss is advised as ~1 lb/week. Doing it slower or faster is ok, too. 0.5lb/week is perfectly fine, especially if you don't have much to lose. Up to 2 lb/week may be sustainable, but unless you're starting from a very high weight, losing more rapidly than that is usually not.

Because 1 lb (0.45 kg) of fat is approximately 3,500 kcal, consuming 500 kcal/day less than you expend would add up to a deficit of 3,500 kcal/week (-500 kcal x 7 = -1 lb fat/week).

There are many websites such as this which can estimate your BMR and TDEE based on your age, sex, height, weight, and activity level. It is only an estimate, as body composition also plays a role, and the energy burned by activity depends a lot on exactly how much and what kind of activity that is, but it can be a good starting point.

Micros

Micronutrients are vitamins and minerals. These do not contain calories, so they do not provide energy, but the body needs them for many physiologic functions, like being cofactors for enzymes or used in the structure of bones and other tissues. For example, scurvy is a disease of connective tissue, which is primarily comprised of collagens, a class of protein. The enzymatic function for collagen production requires vitamin C, so when VitC is lacking, collagen suffers, and the symptoms of scurvy are characterized by the degradation of connective tissue. Micronutrients are found in many places, and a varied diet rich in diverse fruits and vegetables will have greater micronutrient balance and value.

Vitamins can be either water-soluble (B, C) or fat-soluble (A, D, E, K). If a person consumes more of a water-soluble vitamin than their body needs at that time, it will be excreted in urine, and these are not stored for later use. If a person consumes more of a fat-soluble vitamin than they need, the body cannot excrete it as easily. They can be stored in body fat for times when they are more needed, but if severely over-consumed, they may cause illness. However, this is not a risk for most people. In digestion, consuming fat-soluble vitamins with a fat source aids in absorption.

Fat Detail

Fat and sugar have both come under a lot of heat in recent decades. Diets which advise cutting out all fats or carbs completely (or very drastically) are fad diets and not appropriate for the average person. The body needs fats for many functions and cellular structure. If you have a specific medical condition in which this information may not apply to you, consult a professional.

Fatty acids come in a few forms: saturated, monounsaturated, polyunsaturated, and trans. Saturated vs unsaturated describes the molecular structure of the fatty acids by whether they are full of hydrogen atoms or not.

Saturated fats, which are solid at room temperature, are usually found in animal-based sources, such as the fat on a cut of meat or butter. These can come with greater health risks, such as increased LDL cholesterol, but in moderation, they can be alright and come along with other beneficial nutrients.

Unsaturated fats, which are liquid at room temperature, are usually found in plant-based sources, such as avocados, nuts, and olives. These are considered healthier fats, as they get processed and interact with the body differently. Unsaturated fats include the healthy omega-3s and omega-6s found in fish. Both are good, but it's about the balance between them, and omega-3s can be more beneficial than omega-6s. Today, most people get more omega-6 relative to omega-3 than they need, so prioritizing omega-3 is generally a good idea.

Trans fats are hydrogenated oils, for the most part. Scientists take an unsaturated fat and insert hydrogen atoms to create saturated fats for things like butter substitutes or to increase a product's shelf life. Often, this is done because the unsaturated fat and processing is cheaper than the saturated fat equivalent. That process can also occur naturally in some animal-based fats, more like regular saturated fats, but when most people speak of trans fats, they mean the artificial process. These are not good for the body.

Carb Detail

Carbs can be simple, like sugar, or complex, like fiber. Fiber takes longer to digest, so the body's satiety signals (like the hormone leptin) persist for longer after consumption and insulin is released more gradually. Fiber also aids in digestion and can be good for gut health. Simple carbs are absorbed and broken down more quickly, resulting in a sharper spike of insulin followed by a more sudden crash and quicker dissipation of leptin. Some dieticians use the phrase "fiber first" to describe prioritizing a complex carb source before dedicating any leftover calories to simple carb treats.

When people talk about sugar negatively, they mean the added sugars in processed food or homemade treats (granulated sugar is still processed). The natural sugars in fruit are lower per serving than most processed treats and come along with fiber and micronutrients. Don't be scared of fruit sugar; it's worth it.

Protein Detail

"Fiber first" has a lovely sister, "protein first." Especially while losing weight or gaining muscle, protein is very important and should be prioritized. Like fiber, it keeps a person feeling full for longer because of the extended time of digestion and metabolism. It is utilized by muscles, among all your other cells, and a high-protein diet can preserve muscle mass during weight loss or support muscle gain. Muscle cells are extremely protein-dense (they are meat, after all) and need a lot of it.

It's also wise to consume a variety of protein sources. Each will have a different balance of amino acids, which the body uses to make its own proteins. Some amino acids can be synthesized in the body, but others must be consumed directly.

One general rule of thumb is to aim for 1 g of protein for every 1 kg (2.2 lb) of body weight, give or take. If you have a high body weight and/or are in a calorie deficit, eating 1 g/kg like that can mean that a high percentage of your daily calories are coming from protein, which is good. For example, if a 70 kg (154 lb) person wanted to get 70 g of protein, that's 280 kcal from protein per day. If their calorie goal is 1,500 kcal/day, that amounts to 18.67% calories from protein. That is not a very high protein diet, but it's good. Now, imagine if that person were larger; that would demand a higher percentage of kcal from protein and be slightly harder to achieve but very doable.

What I hear recommended for "high protein" is much higher than that, and to reap the benefits of a high protein diet, it needs to be. That recommendation is more like 40% kcal from protein or 1 g protein per 10 kcal consumed, which is a high bar. For physically active people, up to this level or 2 g/kg (like 1 g/lb) is recommended. I'm not saying doing the hard thing is impossible. If realistic and accessible, getting 40% kcal from protein is a great goal. However, there is wiggle room. Less intense high protein diets have been described as 30% kcal from protein, and at that level, there have been demonstrated benefits to blood sugar regulation and hunger control.

Personally, I aim for 20-30% calories from protein because it's realistic for me at the moment. Shooting for an easier, more achievable goal is more beneficial than not trying at all because the lofty goal isn't realistic in your circumstances. I have plans to go harder in the near future, but for me, this is ok for now, and I'm making changes slowly.

If you look at a nutrition label, most nutrients have a line for %DV (daily value), based on a 2,000 kcal/day diet. This is meant to describe the percentage of that nutrient for the day the food provides based on labelling recommendations. However, they aren't a good basis for choices if your goals and those recommendations don't line up. Using a random example of a frozen taquito, this label says it contains 220 kcal/serving (2 taquitos) with 8 g protein (14.5% kcal from protein in this food), which is described as 15% DV. Mathing that out for 2,000 kcal/day, you get 8 g or 32 kcal = 15% of 53.33 g or 213 kcal, which is less than 1 g/kg for most adults and only 10.67% kcal from protein described in that "daily value." Conclusion: adding up your macros based on the label's DV recommendation will likely not serve a high protein goal, and even 20% kcal from protein is an improvement over that suggested DV.