Most people think of muscle building when it comes to protein, but the role of protein in the body spans far beyond its post-workout benefits. Consuming adequate dietary protein is critical for maintaining optimal health, growth, development, and function throughout life (1).
When it comes to weight loss many different diets can be successful, but the protein component of the chosen diet is key and needs to be considered if fat loss is the goal. Studies have confirmed this, finding higher-protein diets are a successful strategy to achieve fat loss and improve body weight management (2). The improvements are thought to be due to proteins effects on appetite control, energy intake, energy metabolism and body mass distribution (3). While it’s important to stress, that as always, there is no one size fits all when it comes to fat loss strategies, it is well accepted that optimal dietary protein intake is one of the key factors influencing an individuals likelihood of achieving and sustaining fat loss and should not be overlooked.
Proteins are made up of building blocks, known as amino acids. The body requires a consistent intake of protein to supply a steady source of amino acids which support the growth and conservation of cells and tissues. Proteins are utilised to form enzymes and cellular transporters, support the regulation and expression of DNA and RNA, create neurotransmitters, function as hormones and facilitate muscle protein synthesis, which leads to the building and conservation of lean mass and improved muscle strength and function (1). In regards to proteins role in fat loss, three primary characteristics of dietary protein have been identified as having a direct influence on body composition. These are satiety, thermic effect and the preservation of lean body mass.
One of the biggest obstacles standing between an individual and fat loss is hunger. Research consistently demonstrates that people are far less likely to adhere to a dietary protocol if they experience feelings of significant hunger (4). As protein is the most satiating of all the macronutrients, dietary strategies that incorporate higher protein intakes typically contribute to greater levels of postprandial satiety and subsequently, a reduced energy intake. This is due to the suppressive effects of dietary protein on hormonal satiety signals and the stimulatory effect of dietary protein on appetite-reducing hormones (5).
The thermic effect of food is the metabolic response of the body to food and refers to the energy required for the digestion, absorption and disposal of nutrients in the food consumed. The greater the thermic effect of a food, the greater the energy expenditure after consuming a meal (6). Studies have demonstrated that foods high in dietary protein have the greatest influence on the thermic effect, contributing approximately twice as much to the estimated thermic effect of food as fat or carbohydrate (7). Although the total effect that the thermic effect has on daily energy and expenditure is reasonably low, in combination with the appetite reducing effects of protein, it still plays an important role in long term fat loss.
In addition to influencing metabolic rate through thermic effect, protein-rich diets further influence metabolism by helping to maintain lean muscle during fat loss. During periods of energy deficit, prioritising protein intake is extremely important to help prevent excessive muscle break down and maintain resting energy expenditure, as well as the conservation of muscle function and performance (8). Multiple studies assessing high vs low dietary protein intake during an energy deficit have found that a dietary protein intake higher than the recommended intake has shown to be more effective than a lower protein intake at preserving lean body mass and fat loss, particularly when combined with exercise (9). What's more, while it is not impossible for the body to store additional protein as fat, the body is far less efficient the body is at storing extra energy from dietary protein as fat than it is as storing dietary carbohydrates and fats.
So, the big question, how much protein does an individual need to consume in order to support fat loss? While that answer is going to vary to some extent from person to person, based on their gender, activity level, life stage and medical history, studies have shown that individuals should be consuming between 1.2 g/kg to 3.1 g/kg per day. Several meta-analyses suggest that athletes and other active adults who are already lean should steer to the higher end of the scale, increasing protein intake to 2.3-3.1 g/kg (11) and those who are overweight or obese require a slightly lower intake of 1.2-1.5 g/kg (12).
While consuming a diet that contains adequate protein is crucial for those wanting to lose fat, like all diets, a high protein diet is only going to be effective if executed in combination with a sensible overall energy intake is, of course, adhered to. Our advice is always food first when it comes to protein, so it’s important to make sure that each meal contains a serve of protein, and high-protein snacks are also considered. Additional protein supplements are beneficial and can be included to help reach protein targets, but should never be selected over whole foods where possible.
This article was written by Holly for The H and P Collective.
(1) Li, J., Armstrong, C., & Campbell, W. (2016). Effects of Dietary Protein Source and Quantity during Weight Loss on Appetite, Energy Expenditure, and Cardio-Metabolic Responses. Nutrients, 8(2), 63. doi: 10.3390/nu8020063
(2) Kim, J., O’Connor, L., Sands, L., Slebodnik, M., & Campbell, W. (2016). Effects of dietary protein intake on body composition changes after weight loss in older adults: a systematic review and meta-analysis. Nutrition Reviews, 74(3), 210-224. doi: 10.1093/nutrit/nuv065
(3) Pasiakos, S., Cao, J., Margolis, L., Sauter, E., Whigham, L., & McClung, J. et al. (2013). Effects of high‐protein diets on fat‐free mass and muscle protein synthesis following weight loss: a randomized controlled trial. The FASEB Journal, 27(9), 3837-3847. doi: 10.1096/fj.13-230227
(4) Gibson, A. A., & Sainsbury, A. (2017). Strategies to Improve Adherence to Dietary Weight Loss Interventions in Research and Real-World Settings. Behavioral sciences (Basel, Switzerland), 7(3), 44. https://doi.org/10.3390/bs7030044
(5) Dhillon, J., Craig, B., Leidy, H., Amankwaah, A., Osei-Boadi Anguah, K., & Jacobs, A. et al. (2016). The Effects of Increased Protein Intake on Fullness: A Meta-Analysis and Its Limitations. Journal Of The Academy Of Nutrition And Dietetics, 116(6), 968-983. doi: 10.1016/j.jand.2016.01.003
(6) Calcagno, M., Kahleova, H., Alwarith, J., Burgess, N., Flores, R., Busta, M., & Barnard, N. (2019). The Thermic Effect of Food: A Review. Journal Of The American College Of Nutrition, 38(6), 547-551. doi: 10.1080/07315724.2018.1552544
(7) Eisenstein, J., Roberts, S., Dallal, G., & Saltzman, E. (2002). High-protein Weight-loss Diets: Are They Safe and Do They Work? a Review of the Experimental and Epidemiologic Data. Nutrition Reviews, 60(7), 189-200. doi: 10.1301/00296640260184264
(8) Kim, J., O’Connor, L., Sands, L., Slebodnik, M., & Campbell, W. (2016). Effects of dietary protein intake on body composition changes after weight loss in older adults: a systematic review and meta-analysis. Nutrition Reviews, 74(3), 210-224. doi: 10.1093/nutrit/nuv065
(9) Longland, T., Oikawa, S., Mitchell, C., Devries, M., & Phillips, S. (2016). Higher compared with lower dietary protein during an energy deficit combined with intense exercise promotes greater lean mass gain and fat mass loss: a randomized trial. The American Journal Of Clinical Nutrition, 103(3), 738-746. doi: 10.3945/ajcn.115.119339
(10) Galgani, J., & Ravussin, E. (2008). Energy metabolism, fuel selection and body weight regulation. International journal of obesity (2005), 32 Suppl 7(Suppl 7), S109–S119. https://doi.org/10.1038/ijo.2008.246
(11) Helms, E., Zinn, C., Rowlands, D., & Brown, S. (2014). 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 Metabolism, 24(2), 127-138. doi: 10.1123/ijsnem.2013-0054
(12) Wycherley, T., Moran, L., Clifton, P., Noakes, M., & Brinkworth, G. (2012). Effects of energy-restricted high-protein, low-fat compared with standard-protein, low-fat diets: a meta-analysis of randomized controlled trials. The American Journal Of Clinical Nutrition, 96(6), 1281-1298. doi: 10.3945/ajcn.112.044321