6 Diets With Harsh Rules

Some weight-loss plans have tough rules, like severe calorie caps and lots of off-limits food.

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Certain weight-loss regimens lay down the law more harshly than others—capping calories at a super-restrictive level, eliminating major food groups, or even requiring followers to give themselves a shot. Some dieters want and need rigid rules. For others, handcuffs are a sure road to failure. U.S. News, which publishes annual Best Diets rankings, took a closer look at 6 plans with strict rules. They're listed in alphabetical order below. (U.S. News has not ranked the 3-day diet, baby food diet, or hCG diet.)

3-Day Diet. Want to drop 10 pounds in three days? Possible, claims the plan, if you follow its ultra-restrictive, low-calorie menu. Breakfast might be black coffee, half a grapefruit, and a piece of toast with a smidgen of peanut butter. Other staples include fruit, veggies, hard-boiled eggs, cottage cheese, tuna (hold the mayo), and saltine crackers. The only approved beverages are water, coffee, tea, and diet soda. Want more? Too bad: You're limited to 800 to 1,000 calories a day, though the government recommends at least 2,000 to 2,400 for moderately active adults. (The 3-day diet doesn't reflect widely accepted guidelines for weight loss, and could lead to nutrient deficiencies, a weakened immune system, and heart problems.)

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Baby Food Diet. Unless you're an infant, subsisting on pureed turkey, carrots, and pears might not sound appealing. But followers believe the portion-controlled jars prevent overeating. Strict adherents exclude "real" food altogether, while some replace just one meal a day with baby food.

Dukan Diet. Fats and carbs are all but squeezed out on this plan, including bread, cheese, and even fruit. All four phases of the Dukan Diet are heavy on do's and don'ts, and even the slightest slip-up is considered destructive. "[S]uccumbing to any other foods, as small as the lapse may be, will be like puncturing a balloon with a needle," warns creator Pierre Dukan, a French physician.

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HCG Diet. It may claim to deliver rapid weight loss—up to 30 pounds a month—but getting there isn't easy. The plan combines drops or injections of hCG, a pregnancy hormone, with just 500 calories a day. That's less than a third of the amount recommended by the government for both men and women, causing medical experts to contend that it could be dangerous. Proponents argue that hCG accelerates weight loss by suppressing appetite and "blasting" fat, while detractors say weight loss is due to the extremely low calorie level—not hCG. The usual menu deems breakfast optional; lunch and dinner call for small amounts of veggies, carbs, and 3.5 ounces of lean, fat-free protein.

Paleo Diet. The premise is to eat only what our hunter-gatherer ancestors did: animal protein and plants. Refined sugar, dairy, legumes, and grains are all out of the question. And forget garnishing meals with seasoning or sauces. This plan offers little variety.

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Raw Food Diet. Most of what raw foodists eat each day are plant-based foods never heated above 115 degrees F. Anything pasteurized, all processed foods, refined sugars and flours, table salt, caffeine, and most store-bought juices, drinks, and milks are off-limits. (Homemade juices using fresh fruits and veggies are OK.)Say hello to fresh fruit and veggies, sprouts, seeds, and nuts, including cashews, sunflower seeds, and raw almond butter.

Next list: Diets That Make You Feel Full

Corrected on : Clarified on 2/16/12: U.S. News has not endorsed any of the listed diets for people who need rules.