We've all heard it said … weight loss is easier on diets high in protein.
Time and again, it's been proven that total calorie intake counts for far more than the mix of calorie sources: fat, carbohydrate (carbs), and protein.
But we still don't know which proportion of fat, carbs, and protein is the most effective – and healthful – for weight control, and whether that varies by gender, age, or genetics.
(Consistently, studies show that high-carb diets are not as healthful as low-carb ones.)
It's become clear that the proportion of fat, protein, and carbohydrates in any diet – including low-calorie diets – can matter hugely to overall health.
And that proportion may affect your success at controlling calorie intake, thanks to the varying metabolic effects of each of the three macronutrients and of different fats and carbs. (All protein exerts similar metabolic effects.)
Putting protein in context
The U.S. Institute of Medicine recommends these intake proportions for adults:
Fat – 20-35% of calories (average 30%)
Protein – 10-35% of calories (average 15%)
Carbohydrates – 45-65% of calories (average 55%)
Hence, a “high protein” diet is defined as one in which 35 percent of calories comes from protein.
So should we expect weight-control or metabolic benefits from low-calorie diets that are particularly high in protein?
The outcomes of a small trial from Australia shed some light on that query … and seem to put another damper on claims that high-protein approaches to weight control work wonders.
Much of the recent research in this realm comes from Australia's Commonwealth Scientific and Industrial Research Organization (CSIRO).
CSIRO scientists have published the results of several small clinical trials testing various proportions of carbohydrate to protein in a defined low-calorie diet … with test ratios of carb calories to protein calories ranging from 3:1 to 1:1.
Three years ago, CSIRO researchers conducted a trial in overweight and obese women, and found that low-calorie diets high in protein improved cholesterol and triglyceride profiles (Clifton PM et al. 2009).
Now, a new study from CSIRO affirms prior indications that there is no particular benefit to low-calorie diets that are particularly high in protein.
Of course, compared with the standard American diet – which is relatively high in carbs – most low-carb diets deliver a higher proportion of protein.
Many of those carbs come from added sugars … and from white flour, which has equally insidious impacts if consumed beyond very modest amounts.
Aussie study finds no weight, body benefit from high-protein-style lean diet
The CSIRO team wanted to see what happened to men put on low-cal/low-fat diets that presented either a moderate proportion of protein, or double that proportion (Wycherley TP et al. 2012).
They recruited 56 men – average age of 45.5 and average BMI of 33.6 kg/m2 – for a 12-week trial.
The men were randomly assigned to one of two low-fat, low-calorie diets (1,671 calories per day), each providing a different proportion (percentage) of protein:
Actually, neither diet was particularly low in fat, compared with the Dietary Guidelines for Americans, which call for fat to contribute 20-35% of daily calories (average 30%).
The High Protein diet provided a protein:carb:fat proportion of 35:40:25, while the Standard Protein diet delivered a protein:carb:fat proportion of 17:58:25.
After three months, the men in both groups had lost an average of 20 lbs (9 kilograms).
And both groups showed similar gains in three standard measures of fitness: relative peak oxygen uptake, knee extensor strength, and peak handgrip strength.
Likewise, the men in both groups showed a significant (four percent) drop in body fat … with a statistically insignificant trend toward more fat loss among the high-protein group.
As the authors wrote, “Altering the carbohydrate-to-protein ratio of an energy-restricted, low-fat diet that achieved similar weight loss and reductions in fat-free mass had similar effects on strength and aerobic capacity in sedentary, overweight and obese men.”
However, as they noted, “… these results are limited to middle-aged men and whether these similar effects occur in younger or older individuals and/or in women and are maintained over the longer-term remains unknown and warrants investigation” (Wycherley TP et al. 2012).
We would point out that there is nothing magic or even desirable about a diet that's low in calories because it is low in fat, instead of being low in carbs.
Average daily fat intake at the upper end of the USDA recommendations (30% of calories) is clearly healthful … as long as you limit the amounts of omega-6 fatty acids and certain saturated fats.
That said, if the average American cut calories by eliminating much of the vegetable oil from their diet, they'd gain health benefits.
Omega-6 fats are essential and healthful in moderation, but the average American consumes three to five times too many, relative to omega-3s, with adverse health impacts.
Brinkworth GD, Noakes M, Clifton PM, Buckley JD. Effects of a low carbohydrate weight loss diet on exercise capacity and tolerance in obese subjects. Obesity (Silver Spring). 2009 Oct;17(10):1916-23. Epub 2009 Apr 16.
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 Oct;19(8):548-54. Epub 2009 Jan 29.
Kreider RB, Rasmussen C, Kerksick CM, Wilborn C, Taylor L 4th, Campbell B, Magrans-Courtney T, Fogt D, Ferreira M, Li R, Galbreath M, Iosia M, Cooke M, Serra M, Gutierrez J, Byrd M, Kresta JY, Simbo S, Oliver J, Greenwood M. A carbohydrate-restricted diet during resistance training promotes more favorable changes in body composition and markers of health in obese women with and without insulin resistance. Phys Sportsmed. 2011 May;39(2):27-40.
Institute of Medicine (IOM). Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Washington (DC): The National Academies Press; 2002
Meckling KA, Sherfey R. A randomized trial of a hypocaloric high-protein diet, with and without exercise, on weight loss, fitness, and markers of the Metabolic Syndrome in overweight and obese women. Appl Physiol Nutr Metab. 2007 Aug;32(4):743-52.
Noakes M, Keogh JB, Foster PR, Clifton PM. 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 Jun;81(6):1298-306.
USDA-HHS. Dietary Guidelines for Americans, 2010 (Released 1/31/11). Accessed at http://www.cnpp.usda.gov/dgas2010-policydocument.htm
Wycherley TP, Buckley JD, Noakes M, Clifton PM, Brinkworth GD. Comparison of the effects of weight loss from a high-protein versus standard-protein energy-restricted diet on strength and aerobic capacity in overweight and obese men. Eur J Nutr. 2012 Mar 11. [Epub ahead of print]
Wycherley TP, Noakes M, Clifton PM, Cleanthous X, Keogh JB, Brinkworth GD. A high-protein diet with resistance exercise training improves weight loss and body composition in overweight and obese patients with type 2 diabetes. Diabetes Care. 2010 May;33(5):969-76. Epub 2010 Feb 11.