Those who are trying to lose weight need and deserve scientifically supported guidance on how to lose weight safely and permanently. So, attempts have been made to analyze these popular diets based instead on currently available scientific data on basic nutrition. The results are interesting. At least they provide some answers on the two most commonly asked questions today: Which of these diets work? And which ones are safe?
Ornish was the only speaker who has published studies comparing people randomly assigned to his eating plan versus a "control" group. The catch, however, is that his Life Choice Program isn’t just a diet. It also gets people to exercise, stop smoking, and participate in stress reduction. So, chances are, diet alone – which Ornish hasn’t studied – didn’t account for his patient’s entire weight loss (25 pounds after one year, which shrank to 13 pounds after five years). Ornish aside, the research cupboard is largely bare. A handful of studies (mostly on normal weight people) has found that when people eat less fat – without trying to cut calories – they lose about five pounds. The few studies do seem like they’re not much evidence for dieters to go on .... especially for people who want to keep weight off over the long haul.
The popular diets "all produce weight loss and they all do it the same way – they cut calories," says Keith-Thomas Ayoob of the Albert Einstein College of Medicine in New York. "The problem isn’t weight loss, but long-term weight management," he stresses. As Tufts University nutrition researcher Susan Roberts says, "I can make anyone lose 20 pounds just by bringing them into our research center for a few weeks." The panelists did agree that there’s really a dearth of good data. When one of the diet book authors claimed lack of funding to explain his lack of evidence, Ayoob retorted, "Ten million books in print and you can’t fund a study?"
1. Is a calorie a calorie? Dr. Atkins, The Zone and Protein Power all claim that calorie for calorie, low carbohydrate diets lead to more weight loss than high carbs diets. Though researchers haven’t tested their specific diets, dozens of studies have found that if you cut any calories – from fat, protein, or carbs – you’ll lose the same amount of weight. "Any differences in how well calories are used by the body are trivial," says Roberts.
2. What’s more important – protein or carbohydrate? There are researches that suggest that what matters isn’t protein vs. carbohydrate but high vs. low-calorie density – that is, calories per pound (or gram or any weight) of food. Books like Volumetrics and The Pritikin Principle argue that the key to losing weight and keeping it off is eating foods with few calories and lots of bulk. Translation: Lots of vegetables, fruits, and only low-fat dairy, poultry, meat, salad dressing, and mayo ... but not low-fat but high calorie foods like fat-free cakes and ice cream.
3. Which diets are safe? When it comes to high-sat-fat, very-low-carb diets, the most obvious problem is LDL ("bad") cholesterol, which rose an average of 18 percent in a 1980 study of 24 people on the Atkins diet. And it’s not just LDL, but the risk of colon and prostate cancers, that could climb when people switch to a diet loaded with sat fat, or, more precisely, red meat.
"I’m not aware of a single, trustworthy piece of evidence that suggests that high-protein diets like Atkins are a healthy way to eat," says Roberts. "The epidemiological studies point to fruits, vegetables, and whole grains as healthy foods." The Atkins diet – like many other weight-loss diets – also runs short on some nutrients. To play it safe, dieters should take multivitamins and mineral supplements as well as calcium.
The PCRM promotes preventive medicine and nutrition, including low-fat vegetarian diets. The organization rated 11 popular diet plans or whether they contained the following:
• at least 25 grams of fiber
• five servings of fruits and vegetables
• no more than 50 mg. of cholesterol
• no more than 30 percent of total calories from fat
• no more than 10 percent of calories from saturated fats
The PCRM gave top ratings to vegetarian diet plans that are high in fiber and low in cholesterol, such as Eat More, Weigh Less by Dean Ornish, MD. The organization gave its lowest rating of "unsafe" to Dr. Atkins’ Diet Revolution, by Robert Atkins, M.D. and The Carbohydrate Addicts Lifespan Program, by Richard Heller, Ph.D. and Rachel Heller, Ph.D.
The US Center for Science in the Public Interest, a private, non-profit health advocacy group, also recently published its own rating of the different diet books. Here is how the Center graded the different weight-reducing plans:
Unacceptable:
Dr. Atkins’ New Diet Revolution
Protein Power
Sugar Busters!
The Carbohydrate Addict’s Diet
Acceptable:
Eat More, Weigh Less
Volumetrics
The Pritikin Principle
Choose to Lose
The Zone
Dieting with the Duchess
Without the availability of good research, however, in most of these popular diet plans, there are still many unanswered questions about their effectiveness and safety.
With all this uncertainty, what’s a dieter to do? Dr. McCally suggests taking a reasonable middle ground – particularly with regard to heart health. "I would just come down in favor of getting as close as you can to a low-fat vegetarian diet," Dr. McCally says. "Everything that we do know suggests that people whose fat consumption is low have less cardiovascular disease than those whose fat consumption is high."