Losing weight is seldom the goal—losing fat is, while preserving muscle. Unfortunately, your body is reluctant to give up its reserves of energy (its fat) and all too quick to metabolize your hard-earned muscle when the caloric deficit gets just a little too high.
Fortunately, what you eat while on a calorie-restricted diet can affect where the weight loss comes from. Diets high in protein, in particular, have benefits with regard to energy metabolism, appetite, overall caloric intake, and muscle retention.
In addition, your body needs to expend 20–30% of the caloric value of protein to metabolize and store it, compared to 5–10% for carbs and just 0–3% for fat. In other words, the thermic effect of food (TEF) is highest for protein. Whether this makes a practical difference in human beings outside of a clinical setting is a much-debated topic, but diets high in protein have also been shown to mitigate the decline in resting energy expenditure (the calories the body burns at rest) caused by calorie-restricted diets, perhaps because protein promotes muscle retention.
A trial randomized 130 overweight people between a high-protein group and a low-protein group. Each day, the high-protein group consumed 1.6 grams of protein per kilogram of body weight (1.6 g/kg, so 0.73 g/lb) and the low-protein group 0.8 g/kg (0.36 g/lb). The trial’s 500 kcal daily deficit led to a weight loss of 9.9–11.2% over a year with no difference between groups, but the high-protein group lost more fat (14.3% ± 11.8%) than the low-protein group (9.3% ± 11.1%), and men more fat than women.
The higher protein intake still benefited women, though, as it did in other trials. When a 10-week trial enrolled 11 obese women to compare a high-protein diet (30% of daily calories as protein) with a high-carb diet (55% of daily calories as carbs), the high-protein diet led to greater weight loss (4.4 kg, so 9.7 lb), most of which was fat (3.7 kg, so 8.2 lb). Relatedly, in a 12-week trial with 100 overweight or obese women, the high-protein and high-carb groups lost the same weight, but the high-protein group lost more fat, which is the same result as in the trial presented in the paragraph above.
Of course, adding exercise can help. In a 16-week trial, 90 overweight or obese women followed the same exercise regimen (aerobic exercise and resistance training) and were randomized to three groups: high protein, high dairy; adequate protein, medium dairy; and adequate protein, low dairy. The first group experienced greater fat loss and muscle gains.
And while the four trials above had enrolled young and/or middle-age women, there’s evidence that postmenopausal women on a calorie-restricted diet also lose less muscle when they eat more protein.
In a 20-week trial, 24 obese postmenopausal women took either 15% or 30% of their daily calories as protein. The 30% group lost less weight (8.4 vs. 11.4 kg, so 18.5 vs. 25.1 lb) but nearly as much fat (7.0 vs. 7.1 kg, so 15.4 vs. 15.7 lb), suggesting greater muscle retention.
Similarly, in a 6-month trial, 31 overweight or obese postmenopausal women (aged 65.2 ± 4.6) were prescribed a diet limited to 1,400 kcal (15% as protein, 65% as carbs, 30% as fat), with one group also taking 50 grams of whey protein twice a day and the other 50 grams of carbs twice a day. The protein group lost more weight (−8.0% ± 6.2%) than the carb group (−4.1% ± 3.6%). The protein group lost more muscle relative to their weight loss, but less muscle relative to their fat loss.
By eating more protein when on a weight-loss diet, you can lose more fat and less muscle.
In a 12-week weight-loss trial, 100 obese people were randomized to high daily protein (2.2 g/kg, so 1.0 g/lb) or low daily protein (1.1 g/kg, so 0.5 g/lb). Both groups lost the same weight, but here again, the high-protein group lost more fat, and it also experienced reductions in LDL-C and total cholesterol not observed in the low-protein group. In another 12-week weight-loss trial with 215 overweight or obese people, a high-protein diet led to greater reductions in fat, total cholesterol, and triglycerides.
Trials usually control for protein quantity rather than quality, but studies show that proteins with a higher percentage of essential amino acids (EAAs) tend to better correlate with fat loss and bone health. Most EAA-rich proteins are animal proteins: meat, fish, eggs, and dairy. The protein in milk is 80% casein and 20% whey protein.
In general, animal proteins are richer in essential amino acids than plant proteins, and so are better for fat loss, but the advantage is small. For fat loss, protein quantity trumps protein quality.
💊 Get unbiased supplement information
- Fact check: does glutamine build muscle?
- Throwdown: plant vs. animal protein for type 2 diabetes
- How can you assess protein quality?
- Whey Protein and Efficiency
- What should you eat for weight loss?
- Is semen high in protein?
- High-Protein Diets Linked to Cancer: Should You Be Concerned?
- Can eating too much protein be bad for you?
- Are there health benefits to a low carb diet?
- 5 little-known facts about protein
- How much protein do you need after exercise?
- Should one gram per pound be the new RDA for bodybuilders?
- Protein Intake Guide
- Does high-protein intake help when dieting?
- Whey vs soy protein: which is better when losing weight?
- How to minimize fat gain during the holidays
- How much protein can you eat in one sitting?
- Do muscle building supplements cause testicular cancer?
- Why do my muscles get sore?
- Why you shouldn't be always taking antioxidants, especially if you want to build muscle
- Does dark chocolate’s epicatechin content promote muscle growth?
- Does ashwagandha increase testosterone?
- Can arachidonic acid work as a bodybuilding supplement?
- Will lifting weights convert my fat into muscle?
- Does Garcinia Cambogia help with weight loss?
- Can hypothyroidism lead to fat gain?
- How do I stay out of "starvation mode?"
- Measuring body fat percentage: It's an accuracy thing
- Does eating at night make it more likely to gain weight?
- Does diet soda inhibit fat loss?
- How to minimize fat gain when you binge
- Be the tortoise or the hare: it doesn’t matter for fat loss
- A compound from beer may help fat loss
- Can one binge make you fat?
- Will carbs make me fat?
- How do I get a six-pack?
- How do I lose fat around my belly?
- Does eating fat make you fat?
- Is diet soda bad for you?
- How important is sleep?
- I have lost significant weight and now have loose skin. How can I tighten up my skin?
- Stepping up weight loss: Can walking help dieters shed fat?
- Low-fat vs. low-carb? Major study concludes: it doesn’t matter for weight loss
- Does aspartame increase appetite?
- Is my “slow metabolism” stalling my weight loss?
- The lowdown on intermittent fasting
- I'm not too tired to stuff my face
- Will eating breakfast keep you lean?
- Do you need to detox?
- Can you lose weight by turning down the heater?
- Does daily weighing help you lose weight?
- Is it OK to skip breakfast?
- Will my breasts shrink with weight loss?
- Exploring chia seeds for weight loss
- Can food have negative calories?
- 3 Science-based steps to curbing your appetite
- A meta-analysis of the effect of glucagon-like peptide-1 (7-36) amide on ad libitum energy intake in humans. J Clin Endocrinol Metab. (2001) C Verdich, et al.
- Dietary protein, weight loss, and weight maintenance. Annu Rev Nutr. (2009) M S Westerterp-Plantenga, et al.
- The effects of high protein diets on thermogenesis, satiety and weight loss: a critical review. J Am Coll Nutr. (2004) Halton TL, Hu FB.
- Thermic effect of food and sympathetic nervous system activity in humans. Reprod Nutr Dev. (1996) Tappy L.
- The role of protein in weight loss and maintenance. Am J Clin Nutr. (2015) Leidy HJ, et al.
- 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) Wycherley TP, et al.
- 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) P M Clifton, K Bastiaans, J B Keogh.
- A controlled trial of protein enrichment of meal replacements for weight reduction with retention of lean body mass. Nutr J. (2008) Leo Treyzon, et al.
- Effects of protein intake and gender on body composition changes: a randomized clinical weight loss trial. Nutr Metab (Lond). (2012) Ellen M Evans, et al.
- Effects of protein vs. carbohydrate-rich diets on fuel utilisation in obese women during weight loss. Forum Nutr. (2003) Idoia Labayen, et al.
- Effect of an energy-restricted, high-protein, low-fat diet relative to a conventional high-carbohydrate, low-fat diet on weight loss, body composition, nutritional status, and markers of cardiovascular health in obese women. Am J Clin Nutr. (2005) Noakes M, et al.
- Increased consumption of dairy foods and protein during diet- and exercise-induced weight loss promotes fat mass loss and lean mass gain in overweight and obese premenopausal women. J Nutr. (2011) Andrea R Josse, et al.
- Lean mass loss is associated with low protein intake during dietary-induced weight loss in postmenopausal women. J Am Diet Assoc. (2008) Melanie J Bopp, et al.
- Effects of dietary protein on the composition of weight loss in post-menopausal women. J Nutr Health Aging. (2008) M M Gordon, et al.
- The effects of a higher protein intake during energy restriction on changes in body composition and physical function in older women. J Gerontol A Biol Sci Med Sci. (2011) Mojtahedi MC, et al.
- Quality protein intake is inversely related with abdominal fat. Nutr Metab (Lond). (2012) Jeremy P Loenneke, et al.
- Short report: Relationship between quality protein, lean mass and bone health. Ann Nutr Metab. (2010) Jeremy P Loenneke, et al.