The healthiest sources of protein according to proven science

This article explains which are the foods that contain protein and presents the healthiest sources of protein according to proven science.

Essential and non essential amino acids

Proteins are the essential building blocks of our body and can be found in muscles, bone, skin, hair and basically in all parts of our organism. Proteins are made of more than twenty amino acids and, given that our body cannot store amino acids, it produces them from scratch or by modifying others.

The following nine are the so called “essential” amino acids because our body cannot manufacture them and so they must come from food: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

“Nonessential” amino acids can be produced by our body, even if we do not get them from the food we eat. These are: alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine.

Healthiest sources of protein

The healthiest sources of protein according to proven science

When food proteins contain all the twenty-plus amino acids needed to make new proteins in the body these are called “complete” proteins and typically these can be found in animal-based foods like meat, poultry fish, eggs, and dairy foods.

When food proteins lack one of more of the nine essential amino acids, then these are called “incomplete” proteins and typically these come from plant-based foods like grains, seeds, nuts, vegetables, and fruits.

Some plant-based foods like quinoa and chia, however, contain complete proteins.

In any case, eating a large variety of plant foods ensures that you get all the amino acids needed to make new proteins also from plant sources, in this way “completing” the aminoacidic profile of their proteins. A classic example is the Italian dish pasta e fagioli (pasta and beans): beans are deficient in methionine and cysteine, two essential amino acids that can be found in higher amounts in whole grains, like whole-wheat bread or pasta, so by combining pasta and beans you can give your body the amino acids that are needed to create proteins. Although dishes like this seem to be perfect choices from a protein intake perspective, you don’t have to study all amino acidic compositions of plant-foods to understand how to pair them to complete their amino acids profiles to provide your body all the essential amino-acids you need. It is sufficient to have a balanced diet that includes a large variety of different foods to ensure your body gets all the essential amino acids to manufacture the body proteins you need, also from plants.

Protein rich foods

Several health organizations agree that the recommended daily intake of proteins is minimum 0.8 grams of protein for every kilogram of body weight for adults. Whilst in underdeveloped countries malnutrition caused by protein deficiency is a huge healthcare issue, in developed countries it’s uncommon for healthy adults to have a protein deficiency. So, under the assumption that you live in a developed country and have regular access to food, you don’t need to bother counting how many grams of proteins you eat; most likely you are already consuming more than enough proteins, probably mainly from animal-based foods if you don’t yet belong to the healthy-eaters club.

Foods that contain protein

Based on a large study that Harvard conducted monitoring more than 130,000 men and women for up to 32 years, the percentage of calories from total protein intake was not related to overall mortality or to specific causes of death. However, the source of protein was important. In fact, when we eat foods, these never come with proteins alone, but they typically also contain other nutrients such as fats, sodium, fiber, and others. It is the food itself, and not just its proteins, that makes a difference when it comes its impact on our health.

Examples of protein foods

In the following table you can see different foods and the nutrients they contain.

Examples of protein foods
Examples of protein foods

Although the above table is meant to give examples of protein foods, it’s always difficult to categorize foods as being carbs, fats, or proteins. In fact, most foods are “packages” of various macro and micro nutrients. It is the whole package that counts, not just the mere amount of macronutrients, such as proteins, it contains.

For example, broiled sirloin steak contains a great amount of complete proteins but these come with a large amount of saturated fat. Ham steak also is a good source of proteins and has much less saturated fat but contains a huge amount of sodium. Grilled salmon is also a great source of proteins and is very low both in saturated fat and sodium. In addition, salmon is a source of omega-3 fats that are very good for the heart. Lentils come with a good amount of proteins and a lot of fiber, and have basically no saturated fat and sodium.

NOTE: In the table, ALA = Alpha Linoleic Acic is the omega 3 fatty acid that is normally found in plant foods such as nuts and fatty seeds like linseed. EPA and DHA = Eicosapentaenoic acid and Docosahexaenoic acid are the omega 3 fatty acids that are normally found in fish, that’s why these are called “marine”.

Discover the healthiest sources of protein

Some sources of proteins are healthier than others. Harvard research provides evidence that eating red meat, and particularly processed red meat, even in small quantities, on a regular basis is linked to an increased risk of heart disease and stroke, cancer, and the risk of dying from cardiovascular disease or any other cause.

A study on 120,000 men and women for more than two decades found that for every additional 85 grams (3 ounce) serving of unprocessed red meat consumed daily, the risk of dying from cardiovascular disease increased by 13%. Processed meat has a stronger negative effect: for every additional 425 grams (1.5 ounce) serving of processed red meat per day (for example one hot dog or two strips of bacon) the risk of cardiovascular disease death increased by 20%. This means that if every person in the study had reduced their total red and processed red meat consumption to less than half than a serving a day, one in ten cardiovascular disease deaths would have been prevented.

Several other studies provide evidence that protein intake from red meat is associated with higher heart disease risk and that diets that replaced red meat with healthy plant proteins decrease such risk.

The ratio of proteins and carbohydrates is also meaningful, with research suggesting that a relatively high-protein intake may be beneficial for health if these proteins are coming from healthy food sources.

A 20-year study of over 80,000 women found that women on a low-carbohydrate diet that were high in plant-based sources of fat and protein had a 30% lower risk of heart disease compared with these who ate high-carbohydrate, low-fat diets. Noticeably, a low-carbohydrate diet high in animal fat or protein did not offer such protection.

Additional evidence from the Optimal Macronutrient Intake Trial for Heart Health (OmniHeart) study observed that replacing some carbohydrates with healthy protein or healthy fat lowered blood pressure and harmful low-density lipoprotein (LDL) cholesterol compared to a higher carbohydrate intake.

The “EcoAtkins” weight loss study compared a low-fat, high -carbohydrate, vegetarian diet to a low-carbohydrate vegan diet that was high in vegetable protein and fat. Weight loss results were similar with the two diets, however the high protein diet produced improvements in blood lipids and blood pressure. 

Eating a lot of red meat and, again, in particular processed red meat also increases the risk of type 2 diabetes. A study found that for each additional daily serving of red meat or processed red meat, risk of diabetes rose 12% for red meat and 32% for processed red meat. The same study observed that replacing one daily serving of red meat with one serving of nuts, low-fat dairy products or whole grains reduced risk of type 2 diabetes by an estimated 16% to 35%.

Another 20-year study investigated the relationship between low-carbohydrate diets and type 2 diabetes in women, finding that low-carbohydrate diets that included a high consumption of fat and protein from vegetables were associated with a lower risk of type 2 diabetes. On the other hand, low-carbohydrate diets with high consumption of animal sources of protein or fat did not show this benefit.

Research also found that when people increased consumption of red meat, they also increased their risk of developing type 2 diabetes during the next four years by 50%, whereas participants who reduced red meat consumption had a 14% lower risk of type 2 diabetes over the following 10 years.

A large study on 289,000 people, found that when frequently eating meats and chicken that are cooked at high temperatures is associated to a 1.5 times higher risk to develop type 2 diabetes, compared to those who ate them less frequently. The study also observed an increased risk of weight gain and obesity on the frequent eaters group.

Red meat and processed red meat are also correlated with cancer. The Nurse’s Health Study and the Health Professionals Follow-Up Study observed that eating one additional daily serving of red meat increase by 10% the risk of cancer death, and one serving of processed red meat increased that risk by 16%.

In 2015, after an evaluation of over 800 studies by a team of 22 scientists from 10 countries, the International Agency for Research on Cancer (IARC), which is part of the World Health Organization (WHO), concluded that eating processed meat is “carcinogenic to humans” and that red meat is “probably carcinogenic to humans.” These conclusions are based on the evidence for colorectal cancer, with data also suggesting a positive association between processed meat and stomach cancer, and between red meat and pancreatic and prostate cancer.

A study on 89,000 women (aged 24 to 43) over a 20-year period found that the risk of breast cancer was 22% higher in those who ate 1.5 servings per day of red meat while in high school, compared to those who only had one serving per week, with each additional daily serving increasing the risk by additional 13%.

Cancer risk from meat consumption is also potentially linked to how the meat is cooked. High-temperature grilling, in fact, creates cancerogenic compounds like polycyclic aromatic hydrocarbons and heterocyclic amines.

Another study of more than 131,000 people from the Nurses’ Health Study and Health Professionals Follow-up Study over 32 years, found that those who eat more red meat, in particular processed red meat, had a modestly higher risk of death, while those who eat a higher protein intake from plant sources had a lower risk.  

Research at the Harvard Chan School of Public Health on over 120,000 people for up to 20 years, found that those who consumed more red meat, processed meat, chicken with skin, and regular cheese gain gained more weight than those who consumed more yogurt, peanut butter, walnuts and other nuts, chicken without skin, low-fat cheese, and seafood.

Evidence-based takeaway on the healthiest sources of protein

For protein-rich food, it’s the source of protein rather than the amount of protein that likely makes a difference for our health: eating healthy protein sources like beans, nuts, seeds, fish, poultry, and eggs in place of red meat and processed meat can lower the risk of several diseases and premature death. Getting most of your proteins from plants may be a very good health bet, in this case just make sure to eat a variety of plant protein-rich food sources so that no essential components of protein are missing. If you enjoy dairy foods, it’s probably a good idea to do so in moderation.

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Chicken is a healthy choice when it comes to protein rich foods, but there are other options too ... (image generated by me with Midjourney AI)