Weight Loss: Diet Dilemma
by Dana Denis, MSPH., RD (topic expert: nutrition)

Obesity continues to be on the rise in the Untied States with over 30% of Americans considered "obese" and almost two-thirds classified as either overweight or obese[1]. The result -- increases in many disease states including heart disease, diabetes, hypertension, and some forms of cancer.

It has been shown that even a 5 to 10% reduction in weight can have beneficial effects on many of these disease states.

In response to this crisis, weight loss diet books are also on the rise. What works? How do you choose? Is the information reliable?

In general most weight loss diets are typically categorized into one of five categories:

Reduced Calorie (e.g. Weight Watchers)
We have all heard that we must reduce our intake (calories and portion sizes) and increase our output (exercise) in order to achieve weight loss. In general, when you reduce your intake by 500 calories below what you expend it will result in weight loss of approximately 1 pound per week. This can be achieved by reducing calories, increasing exercise or better yet, a combination of both. This is thought to be the safest and most reliable form of weight loss.

Low Fat (e.g. Ornish, Pritikin)
This is the traditional diet that has been preached for many years. Fat has more calories per gram than carbohydrate or protein, and only small amounts are necessary to provide its essential nutrients. In addition, since dietary fat was thought to be the leading cause of heart disease, restricting fat was promoted as the best strategy for weight loss for many years. These diets do result in weight loss; however due to the very low fat content (Ornish diet at only 10%), they are very difficult for most people to follow long term.

Low Carbohydrate (e.g. Atkins, South Beach)
These diets gained resurgence over the past few years. They typically start with a very low amount of carbohydrate, less than 20 grams per day, and gradually increase to less than 60 grams per day. These diets are high in fat due to the replacement of carbohydrate with protein and in the case of the Atkins diet, allow unlimited amounts of fat. Clinical research trials resulted in greater weight loss initially: however after one year there was no difference from traditional low fat diets. There was also a reduction in triglycerides and an increase in HDL cholesterol (good cholesterol) with the Atkins diet; however there was also an increase in LDL cholesterol (bad cholesterol). Were the beneficial effects seen due to the type of diet or just the weight lost? The long term effect of this type of diet on cardiovascular disease is still unknown.

Low Glycemic-Index
The glycemic index is a measurement of the effect of carbohydrate on blood glucose (blood sugar) and insulin. A food with a high glycemic index will cause a larger increase in blood glucose. This leads to a higher insulin response, which some believe promotes weight gain. These diets have not produced any difference in weight loss beyond what would be expected from the calorie restriction that accompanies the diet. One recent study showed that the effect of this type of diet on weight loss may be greater in patients who show a larger insulin response when presented with a large amount of glucose (sugar).2 In other words, individuals who are more "sensitive" to carbohydrate may achieve better results with this type of diet.

High Protein
More recently there has been a trend toward replacing some of the carbohydrate in the diet with protein. The protein is increased from 15% to about 30% with a reduction in carbohydrate. Increased protein may enhance satiety and protect lean body mass (muscle). Initial studies resulted in a larger weight loss when compared to the high carbohydrate, low fat diets. This diet differs from the Zone Diet in that every meal does not need to be in the ratio of 30-30-40 (protein - fat - carbohydrate), which increases compliance.

How Did They Compare?
Two studies compared the effects of these various popular diets. The first study compared the Atkins, Ornish, Weight Waters and Zone Diets for differences in weight loss and heart disease risk after 1 year[3]. The participants were both males and females who had pre-existing medical conditions. All diets reduced body weight and several of the risk factors for heart disease, with no difference between the groups. The second study was in nondiabetic, premenopausal women and compared the Atkins, Zone, Ornish and LEARN Diets (The LEARN diet stands for "Lifestyle, Exercise, Attitudes, Relationships and Nutrition" and is a high carbohydrate (55-60%), low fat diet (<20% saturated fat))[4]. At 12 months there was a significant difference in weight loss only between the Atkins and the Zone diets, with Atkins achieving greater weight loss than the Zone diet.

How Reliable is the Information in Diet Books?
An interesting evaluation was published in 2006 on the nutrition and weight loss information published in the South Beach Diet book[5]. The investigators listed all the "nutrition facts" stated in the book then reviewed the medical literature for scientific support of the claims. They found only 33% of the facts stated could be fully supported in the literature, 43% were supported in some studies, but not in others, and for 7% there was no research found.

When looking at a book on diet, review the references of the author. Do they have any education or training in the area of nutrition? What makes them an expert? Does the diet leave out entire food groups which may result in nutritional deficiencies?
Does the diet offer "guaranteed" results?
Does it sound too good to be true?
Do you need to buy special food or products?
These are all "red flags" to be leery of the information.

What has been found to promote success?
A diet that can be "lived with" or maintained over a lifetime will have the greatest success. This may be different for different individuals and that is why no one diet works for all people -- it must be personalized to the individual.

It has been shown that those who regularly include exercise in their program achieve greater success and can maintain the success longer.

Having frequent patient-provider contact can also improve results. A study on weight control from the primary care physician's office showed the involvement of registered dietitians can improve outcome[6].

You can find a dietitian in your area through the American Dietetic Association at www.eatright.com.

1. Ogden, CI, Carroll MD, Curtin LR, et al. Prevalence of overweight and obesity in the United States, 1999-2004. JAMA 2006; 295: 1549-55.
2. Ebbeling CB, Leidbig MM, Feldman HA, et al. Effects of a low-glycemic load vs low-fat diet in obese young adults: a randomized trial. JAMA 2007; 297(19): 2092-2102.
3. Dansinger ML, Gleason JA, Griffith JL, et al. Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction: a randomized trial. JAMA 2005; 293(1): 43-53.
4. Gardner CD, Kiazand A, Alhassan S, et al. JAMA 2007; 29(9): 969-977.
5. Goff SL, Foody JM, Inzucchi S, et al. Nutrition and weight loss information in a popular diet book: is it fact, fiction or something in between? J Gen Intern Med 2006; 21:769-774.
6. Ashley JM, St Jeor ST, Schrage JP, et al. Weight control in the physician's office. Arch Intern Med 2001; 161: 1599-1604.
7. Eckel RH. Nonsurgical management of obesity in adults. N Eng J Med 2008; 358: 1941-50.
8. Clifton P. The science behind weight loss diets. Aust Fam Phys. 2006; 35(8): 580-82.
9. Pritikin Eating Plan. Accessed at www.pritikin.com/pritikin/pritikin_EatingPlan.shtml on May 26, 2008.