Do Diets that are Named After People Work Better?

Abstract & Commentary

Synopsis: Adherence to any diet was the best predictor of weight loss, which predicted degree of improvement in cardiac risk markers.

Source: Dansinger ML, et al. JAMA. 2005;293:43-53.

This was a randomized, single-center, year-long prospective study. Forty participants (160 total) were randomized to each of the following diets: Atkins, the Zone, Weight Watchers, or Ornish. Participants were recruited by newspaper and television ads. To be included, participants had to be overweight or obese, and to have one of the following: elevated fasting glucose, elevated cholesterol, elevated low-density lipoprotein (LDL), elevated triglycerides, hypertension, reduced high density lipoprotein (HDL), or current treatment of hypertension, diabetes, or dyslipidemia. They were not compensated for participating. For the first 2 months, a dietician and physician met with small groups of participants for 1 hour on 4 occasions, and gave diet-specific teaching and advice. All participants, regardless of the diet to which they were assigned, received standard information about exercise, external support, and supplemental vitamins. After the first 2 months, participants no longer had to go to meetings, but were asked to follow their assigned diet according to their own interest level. Outcome measures were assessed at 2, 6 and 12 months, and included weight, cardiac risk factors, exercise, and dietary adherence.

The participants were representative of the US population, and were matched between diet groups. Overall, their mean age was 49 years, and mean Body Mass Index (BMI) at entry was 35 kg/m2.

51% were women, 75% were white, and 13% were smokers. Attrition rate at 1 year was 50% for Ornish, 48% for Atkins, 35% for Zone and for Weight Watchers, and 42% overall. There was no statistically significant difference in weight loss in adherent participants at 1 year, with about 25% of participants overall sustaining a 1-year weight loss of more than 5% of initial body weight. The mean weight loss in kilograms (and pounds) for each diet at 12 months for those who did not drop out was 6.6 kg (14.5 lbs) for Ornish, 4.9 kg (10.8 lbs) for Zone, 4.6 kg (10.1 lbs) for Weight Watchers, and 3.9 kg (8.6 lbs) for Atkins. There was a very strong correlation between self-reported dietary adherence and weight loss. For each group, dietary adherence decreased progressively over time. The most common reasons cited for discontinuation were that the assigned diet was too hard to follow or was not yielding enough weight loss. No adverse events were documented in any participants. All diets resulted in statistically significant but modest improvements in cardiac risk factors, with the exceptions that the Atkins diet did not reduce LDL levels, the Ornish diet did not improve HDL levels, and no diet improved triglycerides, blood pressure, or fasting glucose. The degree of improvement in cardiac risk factors correlated with the degree of weight loss. Dansinger and colleagues comment that "no single diet produced satisfactory adherence rates . . . the higher discontinuation rates for the Atkins and Ornish diet groups suggest many individuals found these diets to be too extreme . . . we suspect that adherence rates and clinical improvements would have been better if participants had been able to freely select from the 4 diet options."

Comment by Barbara A. Phillips, MD, MSPH

What a shocker! People don’t stay on diets! Who knew? This paper is a desperately needed attempt to compare diets in a real life situation. Alas, it confirms what we already knew: it’s the calories, stupid. People who stick with a diet, any diet, lose weight, and people who don’t, don’t. With that shocking revelation, let’s look at a couple of findings that Dansinger et al don’t emphasize much: the attrition rate at 1 year (which predicted weight loss) ranged from 35% to 50%. While this is not statistically significant (P = 0.08) in this relatively small sample, it is likely to be significant in the obese population at large. Two of the diets in this study resulted in roughly a 50/50 chance the patient would drop out, and 2 resulted in only a 1 in 3 chance that the patient would drop out. So, while I agree with Dansinger et al that participants likely found the Atkins and Ornish diets too extreme, I do not agree that outcomes would have been better if the participants had a choice of diets. Participants already do have a choice of diets. Most obese or overweight folks have been through several different diets. And they drop out, not only because dieting is hard and weight loss is slow, but also because there is a confusing array of diets and choices, and the main message (it’s the calories, stupid) gets lost in the hype and the search for the quick fix. My take on this, given that the primary reasons for attrition were that the diets were too hard or weren’t producing fast enough weight loss, is that we have given an inconsistent and unrealistic message. Weight loss isn’t easy, it isn’t fast, and there is not magic diet (or bullet). Losing 10 pounds in a year doesn’t sound like much to folks who have a 100 or more pounds to lose, but the odds are that losing 10 pounds in a year is a huge improvement over what happens if they don’t work at it.

Lest the reason we eat get lost in the shuffle, Eckel points out in the accompanying editorial,1 that attention to nutrition is also important. Another shocker! He reminds us of the recent joint statement of The American Cancer Society, American Heart Association, and American Diabetes Association,2 which focuses on fruits, vegetables, fish, grain and all that boring stuff. Dr. Eckel urges rational eating, for nutrition, which he dubs the "Low Fad" approach.

I think the take home messages are that it is the reduction in calories, not the diet itself that matters, that adherence is a critical factor, that extreme diets are more difficult to adhere to, and that weight loss is hard! I have started giving a very consistent message to my patients about weight loss. Because I think patients need support, because it has long term data on huge numbers of patients and works better than self-help,3 because it is readily accessible in a variety of formats, and because lifetime memberships are available for this lifelong problem, I now recommend Weight Watchers to everyone. And I try to remember to remind them that we eat for nutrition, that weight loss is not easy, and that anyone can lose weight; the hard part is keeping it off.

Dr. Phillips, Professor of Medicine, University of Kentucky; Director, Sleep Disorders Center, Samaritan Hospital, Lexington, KY, is Associate Editor of Internal Medicine Alert.

References

1. Eckel RH. JAMA. 2005; 293: 96-97.

2. Eyre H, et al. Circulation. 2004;109:3244-3255.

3. Heshka S, et al. JAMA. 2003;289:1792-1798.