Dietary protein is an essential macronutrient in the diet that is required to maintain adequate protein levels in the body, and contribute towards muscle protein synthesis, satiety, thermogenesis, and the regulation of blood glucose levels.

Within the body, proteins offer structure, function, and regulation of the body’s tissues and organs. The key roles include:

• Antibodies – These bind and protect against potentially harmful particles, such as viruses and bacteria.
• Enzymes – These carry out the chemical reactions inside of cells and assist with the formation of new molecules by reading the genetic information stored in DNA.
• Messengers – These transmit signals to coordinate biological processes between different cells, tissues, and organs.
• Structural – These proteins provide structure and support for cells.
• Transport – These bind and carry molecules within cells and throughout the body.

The current recommended dietary intake of protein for a healthy individual is 0.8 grams per kilogram of bodyweight. At least, this is the necessary protein intake for metabolic requirements to cover the needs of 97.5% of the population.

Below we’ve listed everything we believe that could be viewed as a positive:

The dangers of excessive protein intake have existed since the days of early American explorers who reported that the excess consumption of lean wild meat led to a condition called “rabbit starvation syndrome” [18].

Since this time and not until very recently, potentially negative effects of a high protein intake have not been discussed. In general, high protein intakes are linked to better health outcomes.

However, recent evidence has suggested that the frequent activation of the anabolic mTOR pathway from protein consumption may increase the rate of aging.

At least in some animal studies, when they are faced with large protein loads, their rate of gastric emptying is reduced and anabolic systems become saturated and unable to deal with an excess of dietary nitrogen [19].

In addition, the inhibition of the mTOR pathway (anabolic pathway) with rapamycin is currently the only known pharmacological treatment that increases lifespan in all animal organisms [20].

Similarly, a reduced consumption of the amino acid methionine, one component of dietary protein, is linked to increased longevity by an lower activation of the growth hormone and IGF-1 signaling pathways [21].

However, although this research is certainly interesting, there is much we do not know and most (if not all) of this research has been conducted in lab settings or on animals. To draw conclusions, human research is a requirement to ensure we have a full understanding of the mechanisms by which amino acids and the mTOR pathway may regulate aging.

This is especially important seen as we know there are certain adaptations that allow us to efficiently adapt to a high protein diet, such as upregulating amino acid metabolizing enzymes such as alanine and aspartate aminotransferases, glutamate dehydrogenase, and argininosuccinate synthetase.

Excess protein is typically broken down by the liver, producing a waste product called urea, which is excreted by the kidneys.

A low protein diet can therefore can ease the workload of the liver and kidneys, which can be beneficial for people with impaired liver or kidney function [22].

This is why the National Kidney Foundation’s recommendations for patients with chronic kidney disease are below those for the overall population – 0.6-0.75 grams per kilogram of bodyweight per day.

Some sources have claimed this reduced workload is also beneficial for those without liver and kidney issues, however, despite these concerns, there is no evidence demonstrating that high protein consumption damages the kidneys or the liver in healthy populations [23] [24].

Another medical concern which might require a low protein intake is for those with genetic disorders that negatively impact protein metabolism. These disorders impair the breakdown of specific amino acids, so reducing protein intake can help minimize symptoms [25] [26].

Below we’ve listed everything we believe that could be viewed as a positive:

Dietary protein possesses the greatest satiety and thermic effect of food of the macronutrients [1]. This means that gram for gram, protein can increase the feeling of fullness much greater compared to dietary carbohydrates and fat.

This is a key reason why high protein diets consistently decrease fat mass whilst conserving muscle tissue during weight loss trials [2].

Large meta-analyses also confirm that high protein diets incur greater weight loss than low protein diets, mainly attributed to the satiating effect of protein [3] [4].

Protein has such a prominent effect on satiety because it regulates the hormones and neurons involved with controlling appetite that effect anorexigenic (appetite-suppressing) and orexigenic (appetite-increasing) neurons located in the brain.

Amino acids are able to increase the release of the appetite-suppressing gut hormones cholecystokinin, glucagon-like peptide 1, and peptide YY – all of which influence the vagus nerve [5] [6] [7] [8].

In addition to increasing the concentration of these hormones such as leptin, protein consumption has shown to decrease the concentration of the appetite-increasing hormones such as ghrelin [9].

Another important aspect of protein intake is that it can increase rates of muscle protein synthesis and regulate anabolic pathways such as mTOR activity.

It is very clear in sport nutrition research that adequate protein intake is necessary to achieve positive muscle protein and nitrogen balance to fully recover and adapt from strenuous exercise.

In fact, athletes have an increased requirement for dietary protein as they need to constantly be repairing and rebuilding damaged muscle tissue from their high activity levels.

For these reasons a low protein diet is not appropriate for those serious about improving their body composition [10] or physical performance [11].

Aging is well-known to lead to progressive bone loss that may result in the development of osteoporosis. This is a very common disease in modern society, with 1 in 4 women over 70 years old having suffered at least one fracture in their lifetime.

Dietary protein is now establishing itself as a nutrient that is critical for proper bone metabolism and to decrease the risk of bone fractures [12].

High protein diets seem to positively affect calcium absorption, bone homeostasis, and bone turnover [13]. Protein is likely able to do this by inducing gastric acid secretion and allowing for calcium ionization and subsequent absorption.

Dietary proteins effect on increasing IGF-1 levels may also have an effect, as IGF-1 can promote osteoblast production and stimulating and is linked to positive outcomes for human bone health [14].

Conversely, low protein diets reduce the production of parathyroid hormone – which regulates calcium content in the blood – and increase the breakdown rate of bone tissue [15].

To combat this newer recommendations actually advise an increase in protein recommendations to over 0.8 grams of protein per kilogram of bodyweight for the aging population. The main reason for this is because protein absorption is slightly inferior in the elderly compared to young healthy individuals, and so they need to compensate for the reduced bioavailability with an increased protein intake to prevent osteoporosis and fracture risk [16].

Now it is worth mentioning that some investigators have proposed the theory that high-protein diets are harmful to bones because calcium phosphate needs to be degraded from bones in order to neutralize the acid load from amino acid metabolism, however this theory has no scientific backing.

The body has a very tightly controlled regulatory system for maintaining the acidity of the blood, such as releasing bicarbonate ions to neutralize acidic by-products, or by excreting excess hydrogen ions through the urine or breath. Even after high-protein meals blood pH remains stable [17].

Modern diets tend to focus meals around high-protein foods like meat or plant-based proteins, and so it can be hard to adapt to a low protein diet.

On such a diet, the focus of meals will require a switch towards grains, vegetables and fruits.

Meat and plant-based proteins should not be avoided, however the frequency of consumption, along with the portion sizes, will be significantly reduced.

Some low protein foods include:

• Fruits: berries, bananas, melon, apple, grapes
• Vegetables: cruciferous vegetables, tomatoes, peppers, corn, broccoli
• Grains: oats, bread, pasta, rice, barley
• Fats: avocados, seeds, vegetable oils, butter

A low protein diet is a diet where protein intake contributes to less than 10% of the total daily calories.

Such a diet is recommended to help treat individuals with impaired liver or kidney function, or genetic conditions that interfere with protein metabolism.

However, protein is a major contributor to a healthy diet and it is not recommended to use a low protein diet if you do not have these medical issues.

A healthy person trying a low protein diet may experience increased hunger, bone issues, and impaired recovery from exercise.