For years, protein has been the top macronutrient stressed in weight loss programming.
Since the mid-1970s, nutritional programs like The Atkins Diet have focused on increased protein intake while reducing carbohydrates to elicit good weight loss results, but little research was available to prove this theory. Recent research is showing proof of the benefits of this macronutrient profile.
A meta-analysis of 24 studies published in The American Journal of Clinical Nutrition examined the effect of the macronutrient profile of diet on weight loss.1 Low-caloric, high-protein diets (>0.8 gm/kg of body weight) were found to be more effective in overall weight loss when compared to a low-caloric, standard-protein diet.
The higher protein diets also performed better in preserving lean muscle mass and preventing a metabolic slowdown during active weight loss.
Theories of why protein helps
Research shows that higher protein diets are effective for weight loss, but why? Many theories in the bariatric medicine community exist and shed light on the impact of protein for weight loss. One theory is diet-induced thermogenesis (DIT) or the thermic effect of food on increasing metabolism.2
The digestion, absorption, transport and storage of macronutrients all have an effect on metabolism. And protein has the highest DIT value, at 15 to 30 percent higher than basal metabolic rate (BMR) energy expenditure. Another theory is protein’s impact on satiety.
Of the three macronutrients (carbohydrates, fat and protein), protein has the highest satiety rating. Protein helps promote satiety because it increases levels of appetite suppressing hormones like glucagon-like peptide-1 (GLP-1) and peptide tyrosine tyrosine (peptide YY). Protein also helps to preserve lean muscle mass, which helps metabolism stay elevated, as muscle tissue burns more calories at rest than fat tissue.
Protein quality matters
Newer research shows that the quality of protein counts for overall health while losing and maintaining body weight, unlike the early high-protein diets that advocated eating higher saturated-fat proteins. A study published in the New England Journal of Medicine showed that eating a diet high in vegetable proteins and vegetable fats and low in carbohydrates can lower the risk of heart disease in women by 30 percent.3
Protein comes in two types: complete and incomplete. Complete proteins contain all nine essential amino acids (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine); these are the amino acids that must be provided to the body by diet. Although most complete proteins are animal-based, there are some vegetable-based complete proteins such as soy, pumpkin seeds, chia seeds and quinoa.
There is a tremendous diversity in the amino acid profile of today’s protein sources. To evaluate the quality of the amino acid profile, the Food and Nutrition Board of the Institute of Medicine (IOM) recommends using the Protein Digestibility Corrected Amino Acid Score (PDCAAS) as the international standard to evaluate proteins.
The PDCAAS represents the quality of protein in terms of its most limiting indispensable amino acid using a standard reference based on estimated average requirements for a healthy population.
The PDCAAS reflects the estimated amount of total protein available for tissue synthesis without drawing indispensable amino acids from any other dietary source or from lean muscle mass.4 The score is based on a scale of 0 to 100 percent (sometimes represented as 0–1.0); with 100 percent (1.0) being representative of the protein providing sufficient amounts of indispensable amino acids for tissue synthesis. See Table 1 for common digestibility scores of commonly used protein sources.
Encourage the conversation
When your patients are sharing details with you about their weight loss and weight management journey, ask questions regarding the quantity and quality of their dietary protein as well as the sources of protein they are ingesting. Overall, protein is crucial for maintaining lean muscle mass during weight loss. It also is critical for compliance as it provides a supporting role in satiety.
Encourage your patients to seek lean sources of animal and vegetable-based protein. Different protein sources have different effects on overall health. Choosing lean meats, poultry and fish are just as important as vegetable proteins found in nuts, legumes and vegetables. Striking a balance among the protein categories should be emphasized.
Tammy Hutchisen, RD, LDN, is the director of clinical and commercial services at Nutritional Resources Inc. (d/b/a HealthWise). She is a member of the Academy of Nutrition & Dietetics, (AND), the AND Weight Management DPG, and the Georgia Academy of Nutrition and Dietetics (GAND). She can be contacted through healthwisenri.com.
References
1 Wycherly TP, Morgan LJ, Clifton PM, Noakes M, Brinkworth GD. Effects of energy-restricted, high-protein, low-fat compared with standard-protein, low-fat diets: a meta-analysis of randomized controlled trials. Am J Clin Nutr. 2012;96(6):1281-1298.
2 Pesta DH, Samuel VT. A high-protein diet for reducing body fat; mechanisms and possible caveats. Nutrition & Metabolism. 2014;11(1):53.
3 Halton TL, Willett WC, Liu S, et al. Low-carbohydrate-diet score and risk of coronary heart disease in women. N Engl J Med. 2006;355(19):1991-2002.
4 Litchfield MD. Protein Nutrition and Bariatric Patients. ADA Weight Management Group Weight Management Matters. 2010;7(3):20-22.
5 Palmer S. Plant Proteins. Today’s Dietitian. 2017;19(2):26-33.
