Protein

Dietary protein is one of the three macronutrients along with carbohydrates and fats. Proteins support almost everything your body does. They play a role as catalysts for nearly every chemical reaction in the body and various individual amino acids also serve double duty as hormones and neurotransmitters.

The human body can synthesize proteins from 20 foundational amino acids. Your body is also capable of making 11 of these (which are called non-essential amino acids). The 9 truly essential amino acids are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

The human genome contains over 19,000 protein-coding genes. From the DNA in the nucleus of a cell, messenger RNA travels to the ribosome with the information to signal synthesis of specific proteins. Your body will produce up to a million different proteins from these amino acids. Some protein molecules are amazingly large and complex. An example is “Titin”, the protein that provides elasticity in muscles and has a molecular weight of up to 3.8 million and contains about 170,000 carbon atoms. The “word” describing the amino acids in Titin is about 190,000 letters long.

“Complete” Dietary Protein & Essential Amino Acids

Before your body can synthesize the proteins it uses, you must eat and digest dietary proteins. After proteins are digested and absorbed into the bloodstream there is an additional step (compared to use of carbohydrates). The liver determines which amino acids remain in the bloodstream and how much of each remains. The liver will break down some of the amino acids into glucose.

All animal sources of protein (flesh, eggs, seafood and dairy products) are “complete” that is they contain all 9 essential amino acids. They are also called “full spectrum” since they contain all 20 foundational amino acids.

The plant sources of complete essential amino acids are:

Tofu, Soymilk, Tempeh
Quinoa
Buckwheat
Spirulina (from blue-green algae)

One can also combine sources of protein to create complete proteins. The most common pairing is grains (rice, wheat, corn) and legumes (beans, lentils, and peas) for example:

Corn & black beans
Whole wheat bread and peanut butter
Rice and lentils

How Much Protein?

The new US dietary guidelines (2025-2030) just increased the recommended minimum protein from 0.8 grams/kilogram of body weight to 1.2 g/kg. This is equivalent to 54.54 grams per 100 pounds of body weight. Two decades ago, the National Academy of Sciences suggested a protein range of 10% to 35% of calories. With a 2,000 calorie-a-day diet this implies between 200 and 700 calories of protein, or between 50 and 175 grams of protein per day. The Cleveland Clinic suggests 25% of your calories from protein. With a 2,000 calorie-a-day diet this implies between 500 calories of protein, or between 50 and 125 grams of protein per day.

However, some sources suggest that the average American eats more than enough protein. Certainly, someone who has kidney issues should consult with their physician before trying to reach the 1.2g/kg value. But for the average person, there is no existing reliable scientific evidence to suggest that there is any danger from eating a higher proportion of protein.

Adjusting your weight for the minimum protein calculation.

The 1.2g/kg minimum measure should be adjusted to reflect an “optimal” percentage of body fat. For men this is about 15% and for women about 20%. Therefore, someone who is overweight or obese should “adjust” their body weight downward to your weight that would exist if you were at the lower (optimal) percentage of body fat. A body scan will tell you your actual percentage of body fat; then you can make the adjustment.

You can approximate this adjustment by using BMI. Start with your actual BMI then reduce body weight until your BMI would be in the middle (for a woman) or the bottom (for a man) of the “normal” range (21.7 middle, and 18.5 bottom of the “normal” range). For example, you are (or were when younger) 5’4” and 160 pounds and you are female. Your BMI is 27.5; you are in the middle of the “overweight” range. The “normal” or “healthy” BMI range is 18.5 to 24.9 and the middle of this range is 21.7. With an on-line BMI calculator, you can determine the weight required to reach the BMI of 21.7 by keeping your height constant and using trial and error to adjust your weight. At 5’4” 125lbs (56.82kg) would yield a BMI of 21.7. At 1.2g/kg your minimum daily protein intake is 68.2 grams.

Who is more likely to need additional protein:

People who are active, especially those engaging in strength training;
Those who are trying to lose weight; and
Older people.

Sarcopenia is the age-related progressive loss of muscle mass, strength and function. The most common cause of sarcopenia is the natural aging process. As you age, your body goes through changes that affect your muscles. You don’t synthesize protein as well, which your muscles need to grow and repair. Changes in hormones like testosterone and insulin-like growth factor (IGF-1) also play a role. Sarcopenia may start in your 30s or 40s but typically worsens between ages 65 and 80. Increasing protein intake (to offset reduced protein synthesis ability) and staying active can help reduce its effects. Strength/resistance training is particularly effective in part since increased muscle mass can also improve protein synthesis.

Intentional or unintentional weight loss may also lead to sarcopenia. This is especially true if you’re NOT doing weight, strength and resistance exercises on a regular basis. Your goal should not be to lose weight per se, but rather to lose fat. If you are losing weight rapidly (more than say 3/4 pound/week) you are at risk of losing muscle mass as you lose weight and you should actively work to retain muscle through strength/resistance training.

Sources of Protein

Many people will struggle to eat 1.2 g/kg of protein per day in the new dietary guidelines. Below is a list of high-protein foods.

Protein grams calories serving size

4 oz lean chicken 31 270 4 oz

4 oz sirloin steak 33 193

4 oz Atlantic salmon 29 206

4 oz drained light tuna 22 98 3.3oz

4 oz tuna steak 28 128

Hamburger lean 4 oz 24 150

4 oz boiled shrimp 20 104

Low fat yogurt 20 150 1 cup

Tofu 4 oz 19.4 165 4 oz

Low fat cottage cheese 13 90 ½ cup

Yellow cheese 6.5 115 1 oz

Protein Supplement 18 75

1 egg 6 72

½ cup black beans 8 114

Lentil Soup 7 155 1 cup cooked

½ cup skim milk 4 42

½ cup soy milk 3 52

½ cup Kefir (1% fat) 5 55

2 oz peanut butter 14.5 295

1 oz yellow cheese 7 120

Kashi Go, dry 12 180 1.25 cup

Keto Bread 2 slice 10 70

Keto Large tortilla 6 100

1 cup almonds 30 828

Quinoa cooked 8 210 1 cup

My optimal weight is about 152lb, at 1.2 g/kg = 82.9 grams/day minimum of protein. As examples, below are protein sources I have included in my meals. This list focusses on protein and ignores the other elements of my diet. As a reminder, the 1.2g/kg is the new recommended minimum of daily protein.

Sample Day Meals PROTEIN FOCUS

Protein g Calories

Day 1

Protein Supplement 18 75
Kashi Go, w skim milk 16 222
3oz Tuna, 2 Keto Bread 17 140
4oz Salmon 29 206
¼ cup almonds 7.5 207

Total day 86.5

Day 2

Protein Supplement 18 75
2 eggs 1 oz cheese 19 260
4 oz chic + keto tortilla 37 370
Healthy Mex Beef Soup 21 340

Total day 95

Day 3

½ cup low F. cot. cheese 13 90
4 oz chicken 31 270
6 oz sirloin steak 49.5 340

Total day 93.5

Day 4

Protein Supplement 18 75
1 cup yogurt 20 150
4oz burger, 2 Keto Bread 34 140
4oz Tuna Steak 28 128

Total day 100

Day 5

Protein Supplement 18 75
1 egg sand 2 keto bread 18 142
4 oz chic + tortilla 37 370
Healthy Mex Beef Soup 21 340

Total day 95

Day 6

Protein Supplement 18 75
1 egg 1 cup black beans 22 186
4oz Tofu 19.4 165
Lentil Soup 2 cup 14 310
1 cup soy milk 6 104
½ cup quinoa 4 105

Total day 83.4

Balance

In the table above protein was the focus. You will need to balance protein intake with other factors such as:

* adequate fiber intake,
consumption of healthy fatty acids (Omega 3, 9, 6)
*reduced red meat consumption
*avoidance of bad fats (trans fats and under 10% calories saturated fat)
avoidance of highly refined foods

The asterisks indicate the categories that may be more difficult for you to balance with increased protein. While it is easier to hit your protein target with red meat - this may create a challenge for you in balancing other sound nutrition dietary principles.

References

All About Amino Acids | Thorne

How Many Human Proteins Are There? - Biology Insights

What Are Proteins? Definition, Types & Examples

Sarcopenia (Muscle Loss): Symptoms & Causes

Here’s How Much Protein You Should Be Eating

High-protein diets: Are they safe? - Mayo Clinic

Should I Eat More Protein? | Tufts Now

https://biologyinsights.com/titin-the-bodys-largest-protein-and-its-role-in-muscle/

What are the 20 amino acid building blocks of proteins? | Britannica

Protein Synthesis – Location, Process, Steps, & Diagram

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