To maintain or reduce body weight, one must control energy intake (and energy expenditure). Current dietary guidelines for the intake of macronutrients established by the Institute of Medicine suggest that 45-65% of total calories should come from carbohydrates, 20-35% from fat, and 10-30% from protein in the diet.
In recent years, diets that focus on protein for fat loss have become popular in the media by promising results of weight loss and decreased fat mass. Some of these diets include the Atkins diet (high protein/high fat), the South Beach diet (low carbohydrate/high protein), the Zone diet (low carbohydrate/high protein), and also diets that are only high in protein without altering other macronutrient intake.
There are advantages and disadvantages of consuming a high protein diet. The important thing to remember is, when fat loss is your goal, overconsuming any macronutrient is going to hinder your efforts. You can’t simply eat more protein to lose more weight. Calories out must exceed calories in, regardless of how high-quality those calories are.
Check out the results of some scientific studies done on the topic of high-protein diets.
Study 1: High-Protein Diets Can Induce Fat Loss
In “A high-protein diet for reducing body fat: mechanisms and possible caveats” (Pesta, 2014) diets high in protein (>30% from total calories or 0.8 grams/kg of body weight) have been shown to potentially promote fat loss. This may be due to the fact that protein increases mechanisms of satiety in the body which helps reduce total energy intake and consequently promote fat loss. At the same time, protein has a higher thermic effect than any other macronutrient which increases the energy expenditure of the body attributed by digestion, absorption, transport, metabolism, and storage of nutrients.
Different types of protein induce satiety in a different way depending on absorption time and nutrient-specific hormone secretion. For example, pea hydrolisate protein has been shown to reduce hunger more effectively followed by whey protein and casein. Upon ingestion of a high protein diet, gut neuropeptides are secreted inducing satiation by decreasing gastric emptying (passage of nutrients along the gastrointestinal tract).
Study 2: Protein Can Reduce Cholesterol While Increasing Satiety
Clifton et al (Clifton, 2009) analyzed data from 215 obese individuals assigned to a 12-week high protein diet. The results show decreased total cholesterol and triglyceride levels as well as abdominal fat. In the study “Comparison of high protein and high fiber weight-loss diets in women with risk factors for the metabolic syndrome: a randomized trial” (Morenga, 2011) women 18-65 years old were randomly assigned a high protein or a high fiber diet for a period of 8 weeks. Results showed that women in both groups had reduced fat mass, BMI, truncal fat, total cholesterol and triglyceride levels, and weight reduction with a modest overall decrease in the high-protein diet group. Participants in the high-fiber diet group, however, reported less hunger and more satiety than those in the high protein group. It has been well documented that high-fiber foods also promote satiety and move slower in the GI tract.
Remember: More Isn’t Always Better
Even though there are some benefits reported in consuming a high protein diet, the long-term effects need yet to be determined. People on high protein diets are advised to choose high-quality protein foods from plant origin to prevent heart disease and increased lipid levels associated with consuming saturated fat present in animal proteins. (Pesta, 2014).
Too Much Protein is Useless to Your Body
Despite the fact that a high protein diet may be necessary for the treatment of certain conditions like protein malnutrition, there is evidence that too much protein could be useless or even harmful to individuals. (Delimaris, 2013).
Overfeeding, in general, will promote weight gain and increased body fat as well, especially if the energy expenditure is lower than the overall calorie intake. This is also true for protein. In a randomized control trial study performed by Dr Bray et al, it was demonstrated that consuming higher amounts of calories from protein results in higher weight gain while maintaining energy expenditure. In the low protein group, 90% of the extra calories were stored as fat, while in the high protein group, 50% of the excess energy was stored as fat.
However less, overfeeding on protein while maintaining the same or negative energy expenditure will result in weight gain and increased fat storage. (Bray, 2012)
Athletes May Be the Exception
But what about athletes, you may ask? There is evidence that protein needs increase when athletes restrict calories (during weight training to reduce body fat or to make weight when wrestling or boxing for example) or have low body fat. When these athletes are in negative energy balance their needs (depending on body composition) can increase up to 3.1 gram/protein per Kilogram of body weight. (HELMS, 2013)
Another is the case of strength athletes and bodybuilders who are interested in stimulating muscular hypertrophy beyond levels required for maintenance. Studies suggest that the protein requirements to maintain nitrogen balance in these athletes ranges from 1.2-2.2 grams/protein of body weight to maintain elevated protein synthesis for greater amounts of muscle tissue and to repair muscle tissue as well. (Wilson, 2006)
For the general population, increased protein diets (especially associated with red and processed meats) can contribute to increased cancer risk, cardiovascular disease, and disease of liver function. Additionally, it has been indicated that high-protein diets can contribute to kidney stones, increased urinary calcium excretion, and can affect glomerular filtration in individuals with renal insufficiency. (Delimaris, 2013). This shows that too much of a good thing can be counterproductive to our health goals and even harmful to our bodies.
1. Ioannis Delimaris: Adverse Effects Associated with Protein Intake above the Recommended Dietary Allowance for Adults. ISRN Nutrition (2013), Article ID 126929
2. Dominik H Pesta and Varman T Samuel: A high-protein diet for reducing body fat: mechanisms and possible caveats. Nutrition & Metabolism 2014
3. Clifton PM, Bastiaans K, Keogh JB: High protein diets decrease total and abdominal fat and improve CVD risk profile in overweight and obese men and women with elevated triacylglycerol. Nutr Metab Cardiovasc Dis 2009
4. Lisa A Te Morenga et al: Comparison of high protein and high fiber weight-loss diets in women with risk factors for the metabolic syndrome: a randomized trial. Nutrition Journal 2011
5. Eric R Helms et al: A systematic review of dietary protein during caloric restriction in resistance trained lean athletes: a case for higher intakes. International Journal of Sport Nutrition and Exercise Metaolism. October 2013
6. Wilson Jacob and Gabriel J Wilson: Contemporary Issues in Protein Requirements and Consumption for Resistance Trained Athletes. Journal of the international society of sports nutrition.2006
7. George A Bray et al: Effect of Dietary Protein Content on Weight Gain, Energy Expenditure, and Body Composition During Overeating: A Randomized Controlled Trial. The Journal of the American Medical Association 2012