As discussed earlier, it is very important to understand total energy balance first. We discussed Resting Metabolic Rate, Exercise Activity, Non Exercise Activity Thermogenesis, and Thermic Effect of Feeding, which combined will yield your Total Daily Energy Expenditure (TDEE.)
A TDEE that is below what we take in will yield weight gain.
A TDEE that is greater than what we take in will yield weight loss.
And while relatively simple in nature, there are outliers that will not always yield the above statements true.
However, assuming all things normal, we need to dig deeper than simply controlling the calorie variable if we want to achieve improved cosmetics and/or improved performance.
This is where macronutrients come into play.
There are three macronutrients that, for the most part, make up our food. Each macro has its own unique “functions” and will comprise a different percentage of total caloric intake based on an individual’s goals.
Protein is an essential nutrient to the body, composed of carbon, hydrogen, and nitrogen. It’s building blocks, or smallest levels, are called amino acids. When amino acids join together, they form peptides that will make up the primary structure of the protein (primary, secondary, tertiary, and quaternary.)
Primary – This is the linear sequence of amino acids found in a polypeptide chain, held together by covalent bonds (peptide bonds) that are made during protein biosynthesis
Secondary – Secondary structures exist on the actual polypeptide backbone chain. They form alpha helices and beta sheets, and are defined by the hydrogen bond patterns between the main-chain peptide groups.
Tertiary – Tertiary refers to the three dimensional structure of monomeric and multimeric protein molecules.
Quaternary – A quaternary structure will be the combination of two or more polypeptide chains that act as a single functioning unit.
Most proteins (in our body structures and in what we consume) will be found in secondary, tertiary, and quaternary forms. But once digested, our body breaks them down to amino acids.
Because we can use amino acids to build new things, we often judge the quality of a protein based on its amino acid composition. The FDA uses a score called the Protein Digestibility Corrected Amino Acids Score. This was an evolution from the previous utilized measures known as the Protein Efficiency Ratio and Biological Value. The PDCAA method is preferred as it is based on the amino acid needs of humans instead of animals.
Amino acids can be grouped into three categories:
- Non-essential amino acids which include alanine, asparagine, aspartate, cysteine, glutamate, glutamine, glycine, proline, serine, tyrosine, arginine, and histidine. These are the 12 amino acids that we can make in our body, and consumption in our diet is not necessary.
- Essential amino acids include phenylalanine, lysine, threonine, tryptophan, methionine, isoleucine, leucine, and valine. You may recognize the final three as the “branched chain amino acids.” The eight essential amino acids can not be synthesized by the body, and must be consumed in our diet.
- Conditionally Essential Amino Acids include arginine, cysteine, glutamine, tyrosine, glycine, ornithine, proline, and serine. These aminos are only essential under certain conditions such as childhood, extreme stress, or the aging process.
It is important to remember that we are always breaking down and rebuilding new proteins. And while our bodies have the ability to store carbohydrates and fats, we can’t store protein in the same way. Amino acid loss is always occurring, and this is why it is essential that we take in enough protein to keep the process of protein turnover happening.
Because of the diverse amino acid sequence of each protein source, it is important to consume a wide variety of protein sources in the diet.
Non processed foods, and seasonal foods will always be preferred, but supplements can certainly help.
And while we typically view animal products as the main protein sources, it is important to note that nearly all foods have some protein in them. Things like broccoli, avocados, potatoes, and nut butters all contain protein that must be accounted for in macronutrient consumption.
Primary protein sources in a diet will be:
- Meats (lean or fatty) like beef, steak, or wild game
- Poultry such as chicken or turkey
- Seafood like wild caught fish and shellfish
- High quality deli meats
- Dairy like greek yogurt or milk
- Beans and Lentils (vegetarian)
- Tofu and Tempeh (vegetarian)
- Protein powders and bars
Protein digestion starts in the stomach, where two of the substances it secretes, hydrochloric acid (HCL) and pepsin create pepsinase, which breaks down the peptide bonds.
The resulting polypeptides and single amino acids are then passed on to the small intestine.
In the small intestine, these polypeptides are broken down by substances called trypsin, chymotrypsin, carboxypeptidase. The result is di and tripeptides as well as free amino acids.
The peptides and amino acids then undergo absorption, where they are either used for energy, synthesize new proteins/enzymes, or they go to the liver.
If they go to the liver, they will either be immediately used (energy production, glucose, ketones, etc.) or they are sent out to the blood stream or to other cells of the body.
Protein Intake Recommendations
There is a lot of controversy around protein intake recommendations, but most of it comes down to specific application.
To start, we need to look at several factors:
- Overall calorie intake
- Whether or not the subject is resistance training
- Body weight and body composition
- Biological age
Let’s begin with the Dietary Reference Intake (DRI). In the United States and Canada, this number is 0.8 grams of protein per kilogram of bodyweight. This number results in about 56g per day for the average sedentary male, or 46g per day for the average sedentary female.
This number may “prevent deficiency,” but it is far from what most would consider optimal.
Ultimately, prescription for protein intake will vary based on goals, but we have seen in most studies that .7-1.2g/lb of body weight is preferential. However, for those individuals carrying a significant amount of bodyfat or that are obese, using target body weight or LBM might be a better number than current body weight.
The more physically active you are, the higher your protein needs will be. Endurance athletes have a higher protein need than sedentary individuals at approximately .5-.65g/lb of body weight.
Also of consideration is that the elderly population typically need to exceed the DRI by up to 50%.
In the mixed modal setting, we see an average prescription come out to 1g/lb of body weight. In the off season, we may see this number higher if body composition goals are prevalent. During season, we will see this number on the low end to ensure there is room in the caloric prescription for carbs and fats to directly fuel the exercise.
A final note – quantity of protein can also be dictated by quantity of protein sparing nutrients (carbs and fats.) When energy intake from carbs and fats are higher, the need for protein is lower. When carbs and fats are lower, the need for protein is much higher.