Great efforts have been put into weight loss research, especially with overweight and obesity prevalence. Many mechanisms have been found to be involved in weight loss such as thermogenesis, a component of the body’s metabolic function in thermoregulation. While thermogenesis can be significantly induced by certain substances, typical food sources can also have an impact on thermogenesis.
High protein diets in general have been associated with increased thermogenic output. Surpassing the induced thermogenic effects of the other macromolecules such as carbohydrates and fats, the degree of thermogenesis can also be affected by the type of protein source. This shows that high protein diets have a greater potential for weight loss.
Thermogenesis is the subsequent conversion of nutrient calories into heat energy as a part of homeostasis - the natural system that maintains the internal, physical, and chemical conditions that support life.
Metabolic functions, especially in the adipose tissues and skeletal muscles, give off heat as a byproduct of their operations. Sufficient heat production for thermoregulation is one of the characteristic differences between warm-blooded and cold-blooded animals.
While the body undergoes thermogenesis at a homeostatic rate, the phenomenon can also be induced by certain thermogenic agents. These are substances that can elicit thermogenesis and subsequently increase basal metabolic rates.
Many substances have been identified to evoke thermogenic effects such as caffeine, ephedrine, bitter orange (p-synephrine), green tea, capsaicin (the active component in chili peppers), forskolin (Coleus root extract), and chlorogenic acid (green coffee bean extract) (1).
These substances have been used to develop thermogenic supplements, colloquially known as thermogenics. These supplements are suggested to aid in weight loss as thermogenesis influences the body to promote fat oxidation. However their efficacy and safety is heavily debated; In some cases ingredients have even been banned by the FDA.
Many different diet paradigms have been suggested for weight loss throughout the years. These include diets such as the paleo diet, the keto diet, the Mediterranean diet, and much more. While some may have presented some degree of success to certain individuals, the majority of these types of diets have been labeled as “fads.”
Today, many experts suggest following a high protein diet. Protein is one of the three major macromolecules (colloquially called “macros”) along with carbohydrates and lipids (fats). As a major macromolecule, protein provides the body with the necessary calories for energy and metabolism.
Furthermore, protein serves specific purposes in the body. While proteins typically take the form of large complex structures, they are essentially made up of building blocks called amino acids. Once ingested, protein is broken down into these molecular building blocks which the body then utilizes for its own protein production.
Protein serves numerous functions in the body. While carbohydrates and lipids serve as efficient energy stores in the body, proteins are considered to be more involved in the body’s functioning since molecules such as enzymes and hormones are made of protein. With the help of these enzymes and hormones, proteins serve a wide array of contributions to the body such as growth, repair, maintenance, and transport.
Typically, a healthy adult should intake approximately 0.66 grams of good quality protein per kilogram body weight per day (2). However, a high protein diet can exceed that amount with no adverse health risks.
Meta-analyses of thousands of studies regarding prospective cohorts, case-control, and interventions have suggested that insufficient evidence supports protein intake with mortality risks, cancer mortality, cancer diseases, and cardiovascular diseases.
Numerous studies provide evidence supporting that high protein diets can help people lose weight. For one, protein food sources have been found to suppress hunger and appetite more effectively after eating. A key factor to weight loss is satiety – the state of satisfactorily fed; fullness.
In weight loss, meals that induce satiety will prevent individuals from wanting to eat more. Eating less food in total will equate to a caloric deficit which is when the body uses more calories than it intakes; This will inevitably result in weight loss.
Studies have been conducted showing that when individuals are left to eat ad libitum (as much as they want), those who consume high protein diets tend to eat lesser quantities of food than individuals eating meals equally composed of proteins, carbohydrates, and fats (3).
This can be attributed to the effect of high protein diets on hormone production, particularly with hormones involved with feelings of hunger and satiety. Ghrelin, the hormone involved with hunger, decreases rapidly after high carbohydrate meals but rebounds very quickly. Comparatively, high protein meals have been observed to decrease ghrelin gradually over a longer period of time (4).
Alternative to ghrelin, which increases in concentration when an individual is feeling hungry, other hormones such as GLP-1 (glucagon-like peptide-1) and PYY (peptide YY) increases when an individual is sated. While high protein diets help reduce ghrelin, they also increase the production of GLP-1 and PYY (5).
Aside from affecting satiety, high protein diets can also influence weight loss through the promotion of muscle production. Total energy expenditure, or the total amount of calories the body burns, can be attributed to three main factors: physical activity, digestion, and basal metabolism. Increased muscle mass not only allows for greater physical activity but also increases basal metabolic rates, thus allowing for greater calorie expenditure.
The thermic response of food intake, called diet-induced thermogenesis, is a general response to food. The heat produced is a result of the various steps involved in nutrient processing (e.g., digestion, transport, absorption, utilization, storage, etc.) (6).
As early as the 1980s, studies have looked into the thermogenic effects of consumed proteins. A 1984 study published in the Annals of Nutrition and Metabolism compared the diet-induced thermogenesis of proteins, carbohydrates, and lipids. The participants were provided with test meals primarily consisting of a certain macromolecule in increasing energy content (1, 2, and 4 megajoules; 238.8 calories, 477.7 calories, and 955.4 calories) (7).
Despite the energy content often associated with carbohydrates, the study found that 1 megajoule of protein produced a thermogenic effect at least three times larger than 1 megajoule of carbohydrate.
The type of dietary protein has also been studied to be a factor to the degree of thermogenesis. A 2011 study published in The American Journal of Clinical Nutrition investigated the thermogenic effects of three different proteins: whey, casein, and soy. Measuring the thermogenic effects in the participants after the test meals, the study observed that whey protein produced a higher thermogenic effect, followed by the casein protein and soy protein respectively (8).
Further studies are required to evaluate the effectiveness of thermogenic protein, particularly the combination of thermogenic substances with dietary or supplementary protein on weight loss.
A pilot study investigated the effects of a thermogenic substance in combination with a supplementary protein. Although the study used mice models, results found that the effects of the thermogenic on body weight and fat were improved when administered in combination with the supplementary protein (9).
While high protein diets have been recommended for weight loss for a long time now, studies investigating its effectiveness in weight loss has only been conducted in the recent years. This field of study has high potential for further investigation, especially when high protein diets are combined with thermogenic supplements.