The Atkins and Paleo diets are unusually low in refined carbs and high in fat and protein.
And both approaches to eating just got a big boost from an unusually well-designed clinical trial.
After one year, those who ate low-carb diets lost more weight and body fat – and had healthier cardiovascular-risk profiles – compared with those who followed low-fat diets.
The people placed on the low-carb diet also gained more lean muscle mass – which is good for metabolic health and weight control – while the low-fat group lost lean muscle mass.
Prior studies have generally found low-carb diets superior to low-fat diets for cardiovascular health, metabolic health, and weigh control (Hession M et al. 2009).
And the results of this unusually rigorous, long-lasting clinical trial validate the wisdom of following an Atkins/Paleo-style diet.
Both eating plans are substantially higher in fats and protein – and lower in carbs (sugars and starches) – than the guidelines issued by U.S. health authorities.
Superior clinical trial finds low-carb beats low-fat for weight loss and overall health
The study was led by Dr. Lydia Bazzano , M.D., Ph.D., from Tulane University in New Orleans (Bazzano LA et al. 2014).
For a full year, her team followed 148 obese volunteers. (Obesity is defined as having a body mass index or BMI equal to or greater than 30 kg/m2.)
More than 85 percent were women, half were African American, their average age was 47, and their average BMI was 35 kg/m2.
The study’s volunteers were randomly assigned to one of two diets:
- Low-carb diet with less than 40 grams of digestible (non-fibrous) carbs per day.
- Low-fat diet with less than 30 percent of daily calories from fat, and 55 percent from carbohydrates.
Both groups were encouraged to eat vegetables and were given general dietary advice … but neither group was given calorie restriction or exercise goals.
(Throughout the study, levels of physical activity and calorie intake were similar in the two groups.)
None had cardiovascular disease (CVD), kidney disease, or diabetes, and they were not allowed to take prescription weight-loss drugs.
All participants met with a dietitian each week for the first month, and then regularly in small group sessions for the rest of the study.
Adherence to their assigned diets was probed at three, six, and 12 months, via surveys in which the participants reported their food consumption for the prior day.
The average calorie content of the low-carb and low-fat diets was 1,448 and 1,527 calories, respectively, and about 80 percent of each group completed the yearlong trial.
Low-fat diet characteristics
The low-fat group ate more grains, cereals and starches, and lowered their total fat intake to less than 30 percent of daily calories, which fits within the 2010 U.S. Dietary Guidelines
Low-carb diet characteristics
The high-fat group increased their total fat intake to more than 40 percent of daily calories, which exceeds official U.S. dietary guidelines
That average daily fat intake violated the 2010 U.S. Dietary Guidelines, which advise adults (19 years or older) to get no more than 35 percent of daily calories from fat.
They were told to favor foods whose fats were primarily unsaturated, like fish, olive oil, and nuts … but were allowed to eat foods higher in saturated fat, such as cheese and red meat.
The low-carb group was also told that it was okay to eat some beans and fresh fruit.
Thus, a typical daily diet might be eggs for breakfast, tuna salad for lunch, and some kind of protein (red meat, chicken, fish, pork or tofu) for dinner, along with vegetables.
While unsaturated fats made up the majority of their fat intake, the low-carb group averaged just over 13 percent of their daily calories from saturated fat … which is more than double the five to six percent maximum advised by the American Heart Association.
Results favored the low-carb diet … dramatically
After a year, there were no differences in the two groups’ blood pressure, total cholesterol, or LDL cholesterol levels.
However, after one year, the low-carb group enjoyed major advantages over the low-fat group:
- Gained lean muscle mass and lost body fat.
- Lost an average of 7.7 pounds more than the low-fat group.
- Blood levels of inflammation markers and triglycerides dropped.
- More “good” HDL cholesterol and a decline in the ratio of bad to good cholesterol.
- Scored lower (better) on the “Framingham heart risk” scale, which calculates the likelihood of a heart attack within the next 10 years.
In contrast, the low-fat group achieved none of those benefits, and suffered blows to metabolic and heart health:
- Shed 7.7 fewer pounds.
- Lost lean muscle mass and gained body fat.
- Saw no improvement in their average Framingham heart-risk scores.
As the authors concluded, “The low-carbohydrate diet was more effective for weight loss and cardiovascular risk factor reduction than the low-fat diet. Restricting carbohydrate[s] may be an option for persons seeking to lose weight and reduce cardiovascular risk factors.” (Bazzano LA et al. 2014)
Dr. Bazzano noted that the results challenge the perception that low-fat diets are always (or ever) better for the heart:
“Over the years, the message has always been to go low-fat. Yet we found those on a low-carb diet had significantly greater decreases in estimated 10-year risk for heart disease after six and 12 months than the low-fat group.” (TU 2014)
Renowned heart-health research Dariush Mozaffarian, M.D., of Tufts University made an important observation in The New York Times:
“To my knowledge, this is one of the first long-term trials that’s given these diets without calorie restrictions. It shows that cutting your carbs helps you lose weight without focusing on calories. And that’s really important because someone can change what they eat more easily than trying to cut down on their calories.” (NYT 2014)
Dr. Mozaffarian added another key insight: “Your balance of lean mass versus fat mass is much more important [to metabolic health] than weight. And that’s a very important finding that shows why the low-carb, high-fat group did so metabolically well.” (NYT 2014)
The primary funding source was the U.S. National Institutes of Health.
Why the two groups’ different cholesterol outcomes matter
For decades, LDL cholesterol has been misleadingly called “bad” cholesterol.
In fact, large, low-density LDL is perfectly healthful, while small, dense LDL is a proven risk factor for cardiovascular disease.
The same LDL concentration in the blood will present a radically different level of risk, based on whether it features lots of small, dense LDL particles or fewer large, fluffy LDL particles.
Diets high in refined carbohydrates tend to raise the number of LDL particles and shift them toward the small, dense variety ... which is a bad thing.
As Dr. Ronald M. Krauss – former chairman of the American Heart Association’s dietary guidelines committee – told The New York Times, “… small, dense LDL is the kind typically found in heart patients and in people who have high triglycerides, central obesity and other aspects of the so-called metabolic syndrome.” (NYT 2014)
But, in the absence of excessive carbohydrate intake, diets long considered “too high” in saturated fat tend to yield large, fluffy LDL particles that are much less likely to clog arteries.
For decades, public health authorities have advocated for diets low in total fat and saturated fats, based on the mistaken belief that they were good for weight control and heart health.
But numerous studies published over the past decade have thoroughly discredited that position, and prove that saturated fat is not a cardiovascular problem for the vast majority of people.
Instead, a recent evidence review found that diets high in omega-6-rich vegetable oils – such as most American’s diets – pose a far greater risk to heart and metabolic health (see “Major Study Exonerates Saturated Fat
The new findings may finally discredit the positions long pushed by Dean Ornish, M.D., and other advocates of low-fat diets.
- Bazzano LA, Hu T, Reynolds K, Yao L, Bunol C, Liu Y, et al. Effects of Low-Carbohydrate and Low-Fat Diets: A Randomized Trial. Ann Intern Med. 2014;161:309-318. doi:10.7326/M14-0180
- Hession M, Rolland C, Kulkarni U, Wise A, Broom J. Systematic review of randomized controlled trials of low-carbohydrate vs. low-fat/low-calorie diets in the management of obesity and its comorbidities. Obes Rev. 2009 Jan;10(1):36-50. doi: 10.1111/j.1467-789X.2008.00518.x. Epub 2008 Aug 11. Review.
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- Hu T, Mills KT, Yao L, Demanelis K, Eloustaz M, Yancy WS Jr, Kelly TN, He J, Bazzano LA. Effects of low-carbohydrate diets versus low-fat diets on metabolic risk factors: a meta-analysis of randomized controlled clinical trials. Am J Epidemiol. 2012 Oct 1;176 Suppl 7:S44-54. doi: 10.1093/aje/kws264.
- Nordmann AJ, Nordmann A, Briel M, Keller U, Yancy WS Jr, Brehm BJ, Bucher HC. Effects of low-carbohydrate vs low-fat diets on weight loss and cardiovascular risk factors: a meta-analysis of randomized controlled trials. Arch Intern Med. 2006 Feb 13;166(3):285-93. Review. Erratum in: Arch Intern Med. 2006 Apr 24;166(8):932.
- O’Connor A for The New York Times (NYT). A Call for a Low-Carb Diet. September 1, 2014. Accessed at http://www.nytimes.com/2014/09/02/health/low-carb-vs-low-fat-diet.html
- Rajaie S, Azadbakht L, Khazaei M, Sherbafchi M, Esmaillzadeh A. Moderate replacement of carbohydrates by dietary fats affects features of metabolic syndrome: a randomized crossover clinical trial. Nutrition. 2014 Jan;30(1):61-8. doi: 10.1016/j.nut.2013.06.011
- Samaha FF, Foster GD, Makris AP. Low-carbohydrate diets, obesity, and metabolic risk factors for cardiovascular disease. Curr Atheroscler Rep. 2007 Dec;9(6):441-7. Review.
- Schwingshackl L, Hoffmann G. Long-term effects of low-fat diets either low or high in protein on cardiovascular and metabolic risk factors: a systematic review and meta-analysis. Nutr J. 2013 Apr 15;12:48. doi: 10.1186/1475-2891-12-48. Review.
- Tulane University (TU). Dieting? Low-carb trumps low-fat for weight loss, heart health. September 2, 2014. Accessed at http://tulane.edu/news/releases/low-carb-trumps-low-fat-for-weight-loss-heart-health.cfm