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Tired of finding yourself unable to lose weight and keep it off? Six diet experts discuss the facts behind real weight loss.
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updated 6/6/2008 8:32:25 AM ET 2008-06-06T12:32:25

For years, diet-book authors, weight loss gurus, and talk-show hosts have proposed a dizzying array of methods for shedding pounds.

There are juice fasts, raw-food programs, and hypnosis techniques; you can eat like a Frenchwoman, a caveman, or Jesus; and according to one recent book, you can even binge one day and fast the next ("Diet only half the time!"). So much for the common sense approach.

Tired of the hype, we turned to six diet experts for the real scoop. These anti-gurus have spent their careers studying what leads to real weight loss. Taking advice from experts who shun the limelight for the lab? That’s a fad we can get behind.

James O. Hill has studied successful dieters for 13 years to see how people lose weight — and keep it off. He is the director of the Center for Human Nutrition at the University of Colorado Health Sciences Center in Denver.

What's the biggest thing you've learned from successful dieters?
Weight loss happens in two stages that require two different approaches. First, there's the losing stage. That's all about food restriction. There's no particular diet that seems to be more effective than another one; it has more to do with individual preference — what you can stick with long-term. The weight-loss stage lasts an average of three to six months. We use 10 percent as a reasonable first goal. After six months, if you get there, you're a success story. If you haven't lost all the weight you want to lose in that time, you're probably not going to do it. If you still have a lot of weight to lose at that point, it's best to take several months to maintain the weight you've shed, then try another six-month diet.

Does exercise help?
Exercise has many health and emotional benefits, but it doesn't make a huge difference when it comes to weight loss. You can restrict your food intake by 500 to 1,000 calories starting tomorrow, but you have to work out for a long time, or at a very high intensity, to burn as many calories.

What's the second stage?
Maintenance. And that's when exercise becomes much more important. By burning a few hundred extra calories a day, you can eat a little bit more, which makes the diet tolerable and easier to maintain. Exercise helps you find a healthy balance between the calories you consume and the calories you burn. Successful dieters typically exercise a lot — 60 to 90 minutes a day. That's not just a short walk. They really prioritize daily, vigorous physical activity.

Are there other habits of successful dieters?
They tend to weigh themselves regularly to stay on track. The scale has been vilified, but it helps you stay focused. They also keep food diaries or count calories. And they are seven-day-a-week breakfast eaters. Eating a meal first thing in the day seems to help people manage hunger better. The typical pattern of obese people is to skip breakfast, have a light lunch, and eat a lot from late afternoon on.

Is there a point at which you're safe — when you'll keep off the weight you've lost?
After three years, you'll know whether you've settled into a routine that allows you to maintain the weight loss. By that point, most of the people in our study say they feel sure they're not going to regain the weight.


Ralph La Forge studies the role of exercise in weight loss and is managing director of the Lipid and Disease Management Preceptorship Program at Duke University Medical Center.

Why is it so hard to lose weight just by exercising?
Unless you're a serious athlete, you just don't burn that many calories. Most people overestimate the amount they've burned during a workout.

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If exercise is part of your weight-loss plan, what's the best type to do?
Aerobic activity is far and away the best, for one simple reason: You burn more calories.

Doesn't strength training build muscle and therefore increase your resting metabolic rate?
That's actually a myth. You'd have to be totally ripped — like, bodybuilder ripped — to get a noticeable bump in your metabolism. Most people burn about one calorie per kilogram of body weight per minute, whereas a bodybuilder burns about 1.2.

What aerobic activities give you the biggest calorie burn?
Cross-country skiing — in nature, not on a machine — is the highest. Outdoor exercise is almost always more strenuous. You encounter variable terrain, which makes you work harder. Running comes after skiing, and walking on hills is probably third. In general, you burn more calories doing a weight-bearing activity that uses lots of big muscle groups. Swimming and biking usually aren't as good because they're not weight-bearing.

Are you better off doing a long, moderate-intensity workout or a shorter, high-intensity one?If you want to lose weight, stay at a moderate pace, because you can go longer and it doesn't wipe you out as much. When you do a high-intensity workout — running or cycling so hard that you can't carry on a conversation — you are so tired afterward that you tend to be lazier for the rest of the day. Instead of going shopping, you lie on the couch. People also tend to eat 20 percent to 25 percent more than normal because they're so hungry.

Don't you enter a fat-burning zone when you exercise at lower intensities? The idea of a fat-burning zone is b.s. In order to burn only fat, you would have to go at such a slow pace that you'd burn only two to three calories per minute. You'd have to walk 50 miles to get a decent workout. It's better to exercise at a moderate pace, so you'll burn some fat and some carbs. Doing that regularly can definitely help you control your weight.

Barry M. Popkin is the director of the University of North Carolina Interdisciplinary Obesity Program, and has studied the causes of the sharp rise in obesity around the world.

To lose weight, what's the single most important change you should make to your diet? Drink fewer caloric beverages. Over the past 30 years, Americans have added about 217 calories a day to their diets in fluids; we consume around one fifth of our calories from beverages.

The problem is that we don't tend to cut our food intake to compensate. People are consuming sports drinks and flavored water and thinking they're getting healthy, but all they're doing is getting fat.

Take vitamin-enhanced drinks: Many are essentially sugar water. You don’t absorb most of the vitamins, and the ones you do absorb, like vitamin C, are plentiful in our diets anyway. You'd be a lot better off eating an orange.

Why don't caloric beverages satisfy our hunger the same way food does?
It's a legacy of evolution. Early humans didn't have sports drinks and juice. All they had was water. If they had filled up on water, they would have starved to death. So our bodies don't respond to liquid calories the same way they do to food.

Is fat really the demon it's been made out to be?
No. The diet industry got everyone to believe that the fat in our diets was making people gain weight, but it's extra calories, no matter what the source. You can lose weight with any diet — Atkins, South Beach, Ornish — as long as you control calories. People who eat a lot of fatty foods tend to weigh more because fat is more caloric, ounce for ounce, than lots of other foods. But that's a portion-control issue.

So big portions are also to blame?
You can't overeat and expect to lose weight, but it’s the size of snacks, not meals, that has changed substantially over the past 20 years. We used to snack on celery sticks; now we snack on bags of chips. The calorie count in one of our snacks is the equivalent of a meal. We've moved from three meals a day to four and a half. Try eating fruit or vegetables with a little low-calorie dressing instead of salty, fatty snacks, and drink water instead of caloric beverages. You'll almost certainly lose weight just from these simple changes.

What's the final verdict on low-carb diets?
They might help some people lose weight, since people do tend to eat fewer calories on that kind of restrictive system. But it's almost impossible to maintain that way of eating over the long haul.

What are dieters' most common psychological pitfalls?
They try to do everything all at once — the extreme-makeover approach. It never works. People set impossible goals, and then they beat themselves up for not being able to sustain the effort. Then they say, "I'm weak-willed," and chuck it all.

So losing weight isn't just for people with a lot of self-control?
It's a fallacy that all it takes is willpower to reshape your body. If you can't learn to speak French in a month, it doesn't mean you're weak-willed; it means you've set an impossible goal. Weight loss does take effort, but as with any project, it also takes a plan. You can set yourself up for success.

For instance, if you always raid the refrigerator when you get home from work because you're starving, you need a plan to prevent that. Have a healthy snack before leaving work, then go out for a run as soon as you get home. And you should keep only healthy foods on hand. It's pretty basic, but so many people fail to take those simple steps — and, as a result, fail at dieting.

Are there psychological traits that distinguish successful dieters from people who lose and regain over and over? The successful ones monitor themselves and they develop solutions to common problems. They've identified what has made them fail before, and they've come up with a plan for dealing with those issues. They might go for a walk when they're stressed, for instance, so they don't turn to food. Their approach is practical and sustainable long-term.

What about the people who feel they are genetically destined to be overweight — can they change?
Biology certainly plays a role in body weight. It's impossible to say how much for each individual person, but it's very important. That said, how you live your life has an influence on your weight, too. If you choose to walk a lot and avoid big portions of high-calorie foods, you're not going to gain a lot of weight. The genetic component means that you have to be realistic about your goals. Sometimes people need to do what they can with weight loss, then let it go and accept the reality of their biology. For instance, weight in the hips and thighs is harder to lose than belly fat. Those fat cells aren't as metabolically active, which just means they're more resistant to change. As a result, a woman can lose weight and still be very curvy.

Louis J. Aronne researches how the body regulates weight and how hormones and other factors affect metabolism. He is director of the New York Comprehensive Weight Control Program at New York–Presbyterian Hospital/Weill Cornell Medical Center.

What's the biggest misconception people have about dieting?
That you can be any weight you want. The average weight loss is 5 to 10 percent of your body weight. Weight is regulated by a complex set of systems in your body, and those are difficult to change. Every person's body is geared to be a certain weight, within a range of maybe 20 pounds or so. Usually the lowest weight you were as an adult is a good indication of your low point. Getting below that is very difficult, but with a healthy, low-calorie diet, you can stay in the low end of your range.

Why is it so easy to gain weight, but so difficult to lose it and maintain that loss?
As you lose body fat, levels of certain hormones, including leptin, drop. The signaling pathway that tells you you're satisfied doesn't work when leptin levels are too low. You don't feel full, which makes you eat more than you should. A drop in leptin also slows your metabolism, so someone who goes from 150 to 130 pounds will have a slower metabolism than someone who consistently weighs 130 pounds.

Besides body weight, does anything else affect leptin? Sleep deprivation can lower leptin levels and increase levels of ghrelin, an appetite-stimulating hormone that's produced in the stomach. That's one reason it's very hard to maintain a diet when you're sleep-deprived.

What about stress?
We're just starting to realize how much emotions affect weight. Stress prompts the body to release cortisol, which makes cells more resistant to insulin. You get excess insulin in the blood, which causes more calories to be stored as fat, especially in your abdomen, and that's associated with heart disease and diabetes.

Claude Bouchard studies identical twins. His work on genes shows why some people gain weight more easily than others. He is the executive director of the Pennington Biomedical Research Center, a research campus of the Louisiana State University System.

When it comes to your weight, how important is genetics?
Extremely important. Genes determine how quickly we feel full when we eat, how inclined we are to be physically active, and how much energy we expend at rest. And we have access to more food than ever before in history, along with fairly sedentary lifestyles. That's why prevention is key. The more weight you gain, the more body fat you have and the more your body hoards that fat. Even a 20-pound gain can change your biology.

Do genetics influence how much you want to exercise?
The Lance Armstrongs of the world may actually be programmed to move more than the average person. But motivation plays a role as well, as does environment. If your gym is close by, you're more likely to go.

Where do you think all this genetic research will lead?
The more we understand the biology of weight regulation, the better able we'll be to design drugs to target specific problems. Right now, the weight-loss drugs we have are like a hammer. They're not subtle or precise, and they have only modest effects. In the future, we should be able to create drugs that target the hormones that regulate appetite, satiety, and metabolism. There are dozens of companies working on such drugs, but it's not easy to find one that works. If it were easy, we'd have one already.

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