The skinny on popular diets

Bestselling diet plans don’t necessarily work any better than do-it-yourself programs.

(This article was first printed in the February 2005 issue of the Harvard Health Letter. For more information or to order, please go to http://www.health.harvard.edu/health.)

If losing weight was one of your New Year’s resolutions and you have already quit your diet, don’t despair. Many off-the-shelf diets come with the seeds of failure — restriction, deprivation, hunger, and cravings — already planted.

Finding an effective eating strategy is serious business if you are considerably overweight and are interested in improving your long-term health. Halting any further weight gain and gradually shedding pounds can have beneficial effects on blood pressure, cholesterol, diabetes, your risk of having a heart attack or stroke, joint pain, and the energy and ability to do everyday activities.

What you really need is a plan you can stick with for many, many moons. It should be as good for your heart, bones, colon, and psyche as it is for your waistline. It should offer plenty of tasty and healthy choices, banish few foods, and not require an extensive and expensive list of groceries or supplements.

Let’s use this yardstick as a way to measure some of the popular diet books.

Low carbs

In the early 2000's, the most popular diets were those preaching the carbs-are-bad gospel. Once seen as the go-to foods for weight loss, carbohydrates such as bread, pasta, and rice were reviled as dietary demons, thanks to the Atkins, SouthBeach, and other low-carb diets. Avoiding carbohydrates, so the thinking goes, forces the body to burn fat.

Does this theory translate into actual weight loss? Yes and no — it depends on the individual and the time period. Some people lose a substantial amount of weight on a low-carb diet, while others lose little and some actually gain weight. And for those who lose, the effects typically aren’t permanent. After a few months, weight loss tends to slow and reverse, just as happens with most other diet types.

Bottom line: Low-carb diets work for some people and not others. There’s no evidence that their short-term effects produce long-term weight loss, while the added expense could lighten your wallet. Equally important, we know little about the long-term health effects of high-protein, high-fat, low-carb diets.

Low fat

Once the main strategy for losing weight, low-fat diets have been elbowed aside by the low-carb frenzy. That’s not necessarily a bad thing, since neither of the two foundations on which low-fat diets were built — fat makes you fat, and fat is bad for the heart — are very solid. Healthy fats can actually promote weight loss, while some fats are good for the heart and eliminating them from the diet can cause problems.

Scores of low-fat diets have been promoted over the years. One of the best known is Dr. Dean Ornish’s Eat More, Weigh Less plan. Since fat contains 9 calories per gram while carbohydrates contain 4, you can theoretically double your food intake without taking in more calories by cutting back on fatty foods and eating more that are full of carbohydrates, especially water-rich fruits and vegetables.

Keep in mind that the Ornish plan doesn’t stop at a whole-grain, vegetarian, very-low-fat (less than 10% of calories from fat) diet, but also includes exercise, stress management, and group support.

Bottom line: Low-fat diets have unquestionably helped some people lose weight and keep it off. They’ve been dismal failures for others, in part because they tend to be less filling, less flavorful, and all around less satisfying than other eating strategies. They also tend to be fairly restrictive about food choices, which can limit your options when dining out.

Correct carbs

Diets such as Sugar Busters! and the Glucose Revolution don’t ban carbohydrates. Instead, they embrace “correct” carbs while shunning “harmful” ones. In a nutshell, this means eating plenty of fruits, vegetables, and whole grains, and cutting back or cutting out refined sugars (white sugar, high-fructose corn syrup, honey, molasses, etc.) and processed grains.

Right-carb diets rely heavily on the glycemic index and glycemic load. In theory, foods with a low glycemic load generate small but steady increases in blood sugar that help stave off hunger. In contrast, the rapid increases in blood sugar and insulin that follow consumption of foods with a high glycemic load are followed by equally steep drops that soon get your internal hunger alarm ringing.

Bottom line: In general, right-carb diets promote healthy eating by focusing on fruits, vegetables, and whole grains. But you don’t really need to rely on the sometimes contradictory glycemic index and glycemic load tables to tell you that. Plans that prohibit refined sugars also make dieting and healthy eating more complicated than it needs to be. Refined sugars aren’t toxic; they just add unnecessary calories.

Perfect proportions and careful combinations

Several diets sell the idea that specific proportions of nutrients or certain combinations of foods are essential to weight loss. If you want to enter The Zone, you must create meals and snacks that contain 9 grams of carbohydrate for every 7 grams of protein and 1.5 grams of fat (40% carbohydrate, 30% fat, and 30% protein).

The Eat Right 4 Your Type diet promotes the wholly unscientific idea that your blood type determines what you should eat, along with how you should exercise, what supplements you need, and what type of personality you have. Following it isn’t easy, since you must remember lists of good and bad foods. It isn’t balanced, something you can tell from the long list of recommended supplements. And it makes it hard to prepare meals for a family with several different blood types.

Bottom line: Proper proportions or correct combinations force you to focus on what you are eating, which helps most people eat less each day. That’s where any weight loss from these diets comes from, not from any nutritional or physiologic secrets the diet developers have uncovered.

Does density matter?

According to the Volumetrics plan, focusing on foods that fill the belly without adding too many calories will help you shed pounds. Foods with a high water content, such as fruits, vegetables, low-fat milk, cooked grains, beans, soups, and stews, get the thumbs up, while high-fat foods like potato chips get the thumbs down, as do dry, calorie-dense ones like pretzels, crackers, and fat-free cookies.

Bottom line: This strategy helps people lose weight the same way most other diets do — it narrows your choices so you take in fewer calories each day. Whether it has a long-term role for weight control isn’t known.

Behavior change

Some people use food for comfort and overeat in response to sadness, loneliness, depression, or any number of other triggers. Breaking an unhealthy relationship with food can help such individuals lose weight. That’s where Dr. Phil’s Ultimate Weight Solution, the Automatic Diet, and others come in.

Dr. Phil offers “seven keys to permanent weight loss” — right thinking, healing feelings, a no-fail environment, mastery over food and impulse eating, intentional exercise, a circle of support, and what Dr. Phil calls high-response cost, high-yield nutrition. The plan offers little advice about nutrition. The Automatic Diet uses behavior modification techniques to reprogram the patterns that work against healthy eating.

Bottom line: If you think that your habits, behaviors, and relationships with other people and with food promote poor eating habits or influence your ability to lose weight or maintain a steady weight, then a behavioral approach makes sense. Combining it with a healthy eating pattern based on sound nutrition would be even better.

The evidence

Given the sheer number of diets promoted over the years and Americans’ long-standing interest in losing weight, it’s appalling how little solid information we have on effective strategies for weight loss.

Surveys of people who have successfully lost weight and kept it off, conducted by the National Weight Control Registry and ConsumerReports, reveal that most did it on their own without resorting to commercial weight loss programs. They tend to chalk up their successes to — drumroll, please — eating less and exercising more. The Registry indicates that participants report taking in an average of 1,800 calories a day and burning an average of 400 calories a day in physical activity, the equivalent of about an hour of brisk walking.

Interestingly, the Registry participants tended to rely on low-fat diets, while the ConsumerReports group relied mostly on low-carb diets.

Another line of evidence about effective weight-loss strategies comes from a few carefully controlled trials in which obese volunteers were blindly assigned to either a standard low-fat diet or a low-carb, high-protein diet. Overall, these trials showed that a low-carb, high-protein diet leads to quicker weight loss than a low-fat diet. In the few studies that lasted for a year, though, weight loss was about the same regardless of diet type. These studies focused primarily on weight, and were too short to track other important consequences of diet, such as heart disease, diabetes, bone strength, and cancer.

The overall results mask some startling individual differences. In one trial, on both low-carb and low-fat diets, some people lost weight while others gained. In the low-fat group, the range was from 53 pounds lost to 31 pounds gained. In the low-carb group, it was from 65 pounds lost to 18 gained.

The take-home lesson is that it is okay to experiment on yourself. If you give a diet your best shot and it doesn’t work, maybe it wasn’t the right one for you, your metabolism, or your situation. Don’t get too discouraged or beat yourself up because a diet that “worked for everybody” didn’t pay off for you. Try another.

Do it yourself

You could also strike out on your own, like thousands of successful dieters before you. You can build your own plan by choosing the smart parts of the diets discussed here.

Or you could try a healthy eating plan based on the best science available, like the one that Dr. Walter Willett, a member of the Heart Letter editorial board, and his colleagues have developed. Its elements include moderation (portion control); eating more fruits and vegetables; cutting back on unhealthy saturated and trans fats and including more healthy unsaturated fats; eating more whole grains and less refined grain; and choosing healthy sources of protein, such as fish, poultry, beans, and nuts.

An overall approach to healthy eating like this one will do more for you in the long term than a diet based on certain foods. One problem with these is that people often think they can eat all they want of the “right foods.”

Dr. Willett’s book, Eat, Drink, and Be Healthy, offers a road map for this strategy.

(This article was first printed in the February 2005 issue of the Harvard Health Letter. For more information or to order, please go to http://www.health.harvard.edu/health.)

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