Low-Fat dieters shed fewer pounds and raised their cardiovascular risk factors; study's length and cafeteria component add weight to findings.
by Craig Weatherby
Judging by the covers of many popular magazines, the question uppermost in Americans' minds remains a familiar one.
“What's the best weight-loss diet?”
It seems that the yearning for a firm answer to this question is exceeded only by tech-related queries such as “Mac or PC?” and “cable or satellite TV?” and, much further down the list, musings about the meaning of life.
Definitive guidance for life's diverse decisions may remain elusive, but new findings from the Harvard School of Public Health appear to advance us toward closure on the “which diet?” question.
For decades, Low-Fat diets were the medically anointed option, hence the choice pushed by the media and favored by the public.
And extreme Low-Fat diets have been touted as heart-healthy—inaccurately, as the new clinical results suggest—by advocates like Dean Ornish, M.D.
Low-Fat diets work for some people, but can produce irresistible cravings and nutritional deficiencies. And their popularity pushed food manufacturers to replace fat with excess salt or sugar, to keep people hooked on their products.
Low-Carb, Atkins-style diets stole the spotlight and gained favor in the late 1990s. But Low-Fat diets retain strong support in conventional medical quarters, despite a dearth of evidence in their favor.
A handful of trials have shown that while Low-Carb and Low-Fat diets can produce comparable weight loss in the long run, the Low-Carb approach usually yields faster weight loss, which may be more rewarding and motivating (Gardner CD et al. 2007; Brehm BJ et al. 2003; Foster GD et al. 2003; Dansinger ML et al. 2005).
A head-to-head trial of Mediterranean versus Low-Fat diets put the former on top (see “Mediterranean Diet Bests Low Fat Rival in Heart Health Face-off”).
And earlier this month, the results of a large Spanish diet-health study found that, as the authors wrote, “Adherence to a Mediterranean-style diet is associated with a reduced risk of diabetes” (Martínez-González MA et al. 2008).
Now, the results of a new American-Israeli study suggest that Low-Fat diets work no better to reduce weight, and may worsen heart health.
Low-Carb and Mediterranean diets offer weight and heart edge
The study in question was called the Dietary Intervention Randomized Controlled Trial (DIRECT).
It was conducted by researchers at Ben-Gurion University of the Negev in Beer Sheva, Israel, and by Harvard researchers at Boston's Brigham and Women's Hospital (Shai I et al. 2008).
The Israeli researchers recruited 322 obese men and women who worked for the same company in Israel and had a body-mass index (BMI) above 30. The average age was 52 and most (86 percent) were male.
The volunteers were divided into three groups, with each assigned to a different diet (Shai I et al. 2008):
- Low-Fat, Calorie-Target Diet: Focus on Low-Fat grains, vegetables, fruits, and beans; limit additional Fats, sweets, high-Fat snacks. Targets: 1,500 calories a day for women, 1,800 for men; under 30% of daily calories from fat, under 10% from saturated fat.
- Low-Carb, No-Calorie-Target Diet: Focus on vegetarian sources of protein and fat; avoid trans fats; no set limit on calories. Targets: Under 20 grams of carbohydrates daily for the first two weeks, under 120 grams a day thereafter.
- Mediterranean-style, Calorie-Target Diet: Focus on fruits, vegetables, whole grains; poultry and fish instead of red meat; added olive oil and nuts to increase intake of unsaturated fats. Targets: 1,500 calories a day for women, 1,800 for men; under 35% of daily calories from fat.
As we reported before, the so-called “Mediterranean” Diet is an idealized version of the diets eaten in the 1950s and 1960s by people in Crete, Sicily, and other rural, generally coastal areas of Greece and Italy (See “Mediterranean Myths”).
In most studies, the “Mediterranean” diet is defined by these criteria:
All of the participants ate lunch—which, importantly, is the main meal in Israeli culture—in the workplace cafeteria, which served the three groups separate meals tailored to their assigned diets.
The volunteers were encouraged to continue their assigned eating patterns at home, they were weighed each month, and their adherence to the diets was validated by a diet questionnaire.
The participants also met with dietitians regularly, and were encouraged to exercise and make other healthy life changes.
After two years, the three diet groups saw these average weight losses, in order of greatest loss:
- Low-Carb diet – 10.3 pounds
- Mediterranean diet – 9.7 pounds
- Low-Fat diet – 6.4 pounds
Given the heavy average weight of the obese subjects at the outset, the differences in weight loss, while substantial, did not reach statistical significance.
Most of the weight loss happened in the first six months.
For unclear reasons, the Low-Carb diet group was the only group given no recommended upper limit on calorie intake.
Despite this distinction, people in the Low-Carb group achieved greater weight loss than those in the other two groups, which may suggest that this approach to dieting is particularly appetite-satisfying.
Study's length and required lunch regimens lend weight to results
The results seem especially significant because of the study's unusual length—two years—and because of the volunteers' high rate of compliance.
Earlier studies generally lasted from six months to one year, and up to half of their participants dropped out.
In contrast, more than eight out of 10 of the DIRECT volunteers kept to their diets throughout the study.
It seems plausible that lunchtime “enforcement” of the assigned diets had an impact on the overall daily dietary patterns within each group.
Some media reports focused on this aspect of the study, but it was not designed to test employer-implemented lunch regimens.
In any case, diet programs like this would apply only to companies or institutions with cafeterias and a critical mass of employees demanding certain diets at lunch.
Harvard press release downplays key findings
The authors of a press release from Harvard included a statement that distorts its results (HSPH 2008):
“The lesson from DIRECT is not that Low-Carb or Mediterranean-type diets are better than Low-Fat diets, though you will undoubtedly see that spin in some media reports and ads for Atkins and South Beach diets” (HSPH 2008).
While the weight loss differences were not large, the Low-Carb and Mediterranean-type diets certainly produced outcomes “better” than the Low-Fat diet, in terms of both pounds shed and overall health.
In fact, the Low-Fat diet made the weakest showing in terms of both weight loss and cardiovascular impacts. As the press release itself said:
“…a Low-Carbohydrate approach or a Mediterranean-type eating pattern are just as good as a Low-Fat diet for losing weight. They may also be better for preventing or controlling heart disease and diabetes.”
All three groups enjoyed similar reductions in average waist size and blood pressure, but average LDL (“bad”) cholesterol levels did not change significantly in any group.
But where differences appeared, the results favored the Low-Carb and Mediterranean diets (HSPH 2008):
- “The volunteers following the Low-Carb diet had the biggest drops in triglycerides … and the biggest increases in protective HDL cholesterol. Both of those changes would be expected to protect against heart disease.”
- “Those following the Mediterranean diet showed the biggest reduction in Low-grade inflammation, a process linked to the development of heart disease. Among the volunteers with diabetes, the Mediterranean diet yielded better fasting blood sugar and insulin than the other two diets.”
The Low-Carb and Mediterranean diet groups also enjoyed three other advantages:
- The Low-Carb diet group had the greatest increase in average levels of “good” HDL cholesterol.
- The reduction in the ratio of total cholesterol to HDL cholesterol was 20 percent in the Low-Carb group but only 12 percent in the Low-Fat group.
- Both the Mediterranean-diet and Low-Carb groups achieved Lower blood levels of C-reactive protein, which is a leading medical measure of arterial inflammation and heart attack risk.
Writing in Journal Watch (Cardiology), Harlan M. Krumholz, M.D., made this cogent comment, which contradicts any implied medical equivalence among the three diets:
“In this study, the Mediterranean and Low-Carbohydrate diets were associated with greater weight loss and more favorable metabolic effects than was the Low-Fat diet. These findings lend evidence to support recommending these diets as alternatives to the Low-Fat diet” (Krumholz HM 2008).
And the study's authors also suggested—too weakly, in this writer's view—that “metabolic considerations” might lead patients or doctors to choose a Low-Carb or Mediterranean-style calorie-cutting diet over a Low-Fat calorie-cutting diet.
Given their metabolic advantages, Low-Carb and Mediterranean-style diets seem clearly preferable, barring uncommon medical contraindications or strong personal food preferences.
Note: The DIRECT study was supported in part by the Dr. Robert C. and Veronica Atkins Foundation.
The late Dr. Atkins pioneered Low-Carb, high-protein “Atkins” diets in several bestsellers and sold related products.
Unfortunately, Dr. Atkins generally failed to distinguish among protein foods with very different Fat profiles.
For example, he made no distinction between grain-fed pork, which is very high in pro-inflammatory omega-6 Fats, and wild Salmon, rich in anti-inflammatory, heart-healthy omega-3s.
- Brehm BJ, Seeley RJ, Daniels SR, D'Alessio DA. A randomized trial comparing a very Low Carbohydrate diet and a calorie-restricted Low Fat diet on body weight and cardiovascular risk factors in healthy women. J Clin Endocrinol Metab. 2003; 88:1617-23.
- Dansinger ML, Gleason JA, Griffith JL, Selker HP, Schaefer EJ. Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction: a randomized trial. JAMA. 2005; 293:43-53.
- de Lorgeril M, Salen P, Martin JL, Monjaud I, Delaye J, Mamelle N. Mediterranean diet, traditional risk factors, and the rate of cardiovascular complications after myocardial infarction: final report of the Lyon Diet Heart Study. Circulation. 1999; 99:779-85.
- Foster GD, Wyatt HR, Hill JO, et al. A randomized trial of a Low-Carbohydrate diet for obesity. N Engl J Med. 2003; 348:2082-90.
- Gardner CD, Kiazand A, Alhassan S, et al. Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women: the A TO Z Weight Loss Study: a randomized trial. JAMA. 2007; 297:969-77.
- Harvard School of Public Health (HSPH). Many Paths to Successful Weight Loss. Accessed online July 20, 2008 at http://www.hsph.harvard.edu/nutritionsource/healthy-weight/weight-loss-study/index.html
- Krumholz HM. The Diet Debate: Mediterranean, Low-Fat, or Low-Carb? Journal Watch Cardiology. July 16, 2008. Accessed online July 20, 2008 at http://cardiology.jwatch.org/cgi/content/full/2008/716/1
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- Martínez-González MA, de la Fuente-Arrillaga C, Nunez-Cordoba JM, Basterra-Gortari FJ, Beunza JJ, Vazquez Z, Benito S, Tortosa A, Bes-Rastrollo M. Adherence to Mediterranean diet and risk of developing diabetes: prospective cohort study. BMJ. 2008 Jun 14;336(7657):1348-51. Epub 2008 May 29.
- Shai I, Schwarzfuchs D, Henkin Y, Shahar DR, Witkow S, Greenberg I, Golan R, Fraser D, Bolotin A, Vardi H, Tangi-Rozental O, Zuk-Ramot R, Sarusi B, Brickner D, Schwartz Z, Sheiner E, Marko R, Katorza E, Thiery J, Fiedler GM, Blüher M, Stumvoll M, Stampfer MJ; Dietary Intervention Randomized Controlled Trial (DIRECT) Group. Weight loss with a Low-Carbohydrate, Mediterranean, or Low-Fat diet. N Engl J Med. 2008 Jul 17;359(3):229-41.
- Tuttle KR, Shuler LA, Packard DP, et al. Comparison of Low-Fat versus Mediterranean-style dietary intervention after first myocardial infarction (from The Heart Institute of Spokane Diet Intervention and Evaluation Trial). Am J Cardiol. 2008; 101:1523-30.