The Crash Dieting Secret

  With summer one month away, you may think it’s too late to get in bikini-ready shape. But new research shows that when it comes to dieting, slow-and-steady doesn’t always win the race.  

05.18.09 5:47 AM ET

Here’s a sobering thought: Summer is a month away, and the diet you’ve been meaning to embark on since January remains in the early planning phases. A crash diet seems to be your only option—but aren’t crash diets ineffective routes to sustainable weight loss?

Not if you approach them correctly. A healthy, low-calorie diet can work wonders, even in just a few weeks, and clinical experience shows that somebody with a serious commitment to weight loss can lose up to 20 pounds—and two to three clothing sizes—in a mere eight weeks. That’s a lot of weight, and an enormous change in appearance for most of us. Best of all, according to the latest research, a hard-and-fast approach to dieting, if done right, can yield results that will probably stand the test of time just as well as the long-term diets that emphasize incremental gains.

For many people, fast weight loss actually appears to bring long-term success equivalent to more gradual weight-loss programs—reason for procrastinators everywhere to rejoice.

The conventional wisdom about more rapid weight loss leading to rapid rebound is, happily, not being supported by research. For many people, fast weight loss, if achieved with a healthy, calorie-cutting food-based diet, actually appears to bring long-term success equivalent to more gradual weight-loss programs—reason for procrastinators everywhere to rejoice. In fact, for some people, healthy crash dieting may work even better than a diet that lasts all year. A recent study from my lab at Tufts University found that the slow-and-sensible approach seems to be sustainable only by those folks who are not sidetracked by rich food, free food, and other common challenges in daily life.

What about even faster weight loss? You know those diets: the ones that promise to dissolve 36 pounds in one month, or 18 pounds in four days. Unfortunately for anyone planning on stretching out their new-and-improved bod on a chaise longue this weekend, such diets are pure snake oil. Crash dieting can work, but there’s a threshold. It’s a physiological fact that the human body is only capable of losing a maximum of about 3.5 pounds of actual fat per week, even if you eat nothing at all. Greater weight losses than this may occur for a week or two if you put yourself through the wringer of fruit-juice fasts, purges, or Master Cleanses, but you won’t lose any more fat—just water, intestinal contents, and sometimes muscle thrown in for good measure. That’s the kind of weight that will bounce right back after a barbecue or two.

The only crash diet that truly works is one that allows you to lose real fat and lose it as fast as sustainably possible. But how do you make it work well and, in particular, how do you avoid common concerns like plateaus? By cutting enough calories. It’s a little-known fact that many popular diets don't cut as many calories as really needed, because they don't deal with the hunger factor well enough to go further. These diets do achieve short-term weight loss with a combination of small calorie cuts and low-sodium meals that cause water excretion, but once water balance stabilizes, you plateau and feel like your dieting is getting nowhere.

So the first principle of successful dieting is to get calories low enough to reliably cause ongoing, serious fat loss. In practice, this means getting daily caloric intake down to something like 1,200 calories a day if your starting weight is 120-160 pounds, or to 1,800 a day if your starting weight is 200-240 pounds. Several research studies have shown that at this level of intake, calorie requirements don't decrease anywhere near enough to make you plateau, so fat continues to be pulled from fat cells and real fat weight continues to slide off.

The second principle involves eating the right foods at the right time; if you don’t, counting calories won’t cut it because you will be too hungry or unsatisfied to see it through. Based on a number of research studies, it is now clear that liquid calorie diets do work, but they are so desperately boring few people can stick to them. To enjoy yourself more, go the real-food route and maximize benefits by making sure that every meal and snack you eat combines at least two of these properties that numerous research studies have shown cut hunger and boost satiety: high fiber, high protein, high volume, and low glycemic index carbs. And remember to keep those good foods coming—eating three meals and two-to-three snacks every day, and spreading calories fairly evenly from morning to night, is about as important as choosing the right foods when it comes to maximally suppressing hunger.

Best Foods for Keeping Hunger Down and Satisfaction Up



High-fiber cereals, e.g. FiberOne, Trader Joe’s High Fiber Cereal with milk, Greek plain yogurt, sugar-free ice cream, berries, even salads

Very high fiber

Green and raw vegetable salads with vinaigrette or light dressing

Very high volume; lots of natural variety

Cooked non-starchy vegetables such as broccoli, mushrooms, zucchini

High volume; high fiber.

White fish such as cod, haddock

Low in calories, high in protein; highest satiety of any protein food.


Portable sweet-tasting snack; lowin calories, high in fiber; hard to eat too quickly; wide variety.

Berries, e.g. raspberries, strawberries, blackberries

Low in calories, high in fiber and easy enjoyment. Frozen berries are a great standby.

Legumes in entrees, soups and salads

Very high in fiber and volume; wide variety, good taste (when done right).

Low-carb, coarse, high-fiber, high-protein and barley breads

More filling and sustaining than regular breads; high protein and higher fiber.

Bottom line: Stock up on the good foods that help with weight control, and then keep those calorie counts down. Start now, and there’s still time to put your new body on a collision course with summer.

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Dr. Susan Roberts is a professor of nutrition and professor of psychiatry at Tufts University, and the author of a new approach to weight loss called The Instinct Diet. Dr. Roberts endorses specific food products in this article but does not take any money from food companies for her endorsements.