Lose Weight and Keep It Off

The truth about popular diets

By now you know that there’s not one magical diet guaranteed to melt off the pounds. It’s also helpful to bear in mind that many diets don’t live up to their claims and, in some cases, may even spell trouble for your health. Here’s a quick overview of a few popular diet and diet trends. You can find a more indepth analysis in another Special Health Report from Harvard, The Diet Review: 39 popular nutrition and weight-loss plans and the science (or lack of science) behind them.

Detox diets, cleanses, and juice fasts. Detox diets and cleanses are often laxative concoctions that can cause electrolyte imbalances and dehydration. And they’re completely unnecessary. Your body has its own in-house detoxification system: your liver and your kidneys. These two organs work tirelessly to dismantle and remove impurities from your body, so toxins never have the chance to accumulate. As for juice fasts? Vegetable juice can be a good way to bump up your produce intake, but it shouldn’t be the mainstay of your diet. With a juice diet, you’re missing out on fiber, not to mention the protein your body needs to support your liver and kidneys. Since all of these diets are extremely low in calories, they can slow your metabolic rate. Then, as soon as you begin to eat normally again, you’re likely to regain the weight that you lost.

Gluten-free diets. Gluten is a protein found in certain grains, such as wheat, barley, and rye. Some people—namely, those with either an autoimmune condition called celiac disease, or with non-celiac gluten/wheat sensitivity—need to eliminate gluten from their diets for medical reasons. A gluten-free diet allows all foods that don’t contain gluten, including fruits, vegetables, gluten-free whole grains, meat, poultry, fish, eggs, and dairy. This diet can be very healthful. However, when it comes to weight loss, gluten-free diets provide no advantage whatsoever. What’s more, specially formulated gluten-free foods— such as gluten-free breads and pasta—are often high in carbs, refined sugars, and calories.

Intermittent fasting. There are several forms of intermittent fasting, some more extreme than others— such as skipping food every other day. The most robust studies show intermittent fasting does not have a clear weight-loss advantage over simply limiting daily calorie intake. But studies support some metabolic benefits for “time-restricted eating,” which limits your daily “eating window.” Many people keep their window to eight hours, with an overnight fasting period of 16 hours. For example, if you eat breakfast at 8 a.m., you would not have any food after 4 p.m. a few days per week, or even every day. This practice, especially if breakfast is larger and dinner is smaller, helps synchronize the body’s circadian rhythms and promotes metabolic health.

Ketogenic diet. This diet is 75% to 90% fat, 10% to 20% protein, and up to 5% carbohydrates. It forces your body to burn fat instead of glucose (sugar) for fuel. In studies, the keto diet shows some short-term advantage for weight loss and blood sugar management, but there are no long-term studies to offer evidence that people keep the weight off.

Paleo diet. This plan focuses on whole foods such as meat, fish, poultry, eggs, fresh fruits and vegetables, and nuts and seeds, plus coconut, olive, and flaxseed oils. At the same time, it excludes several important food groups, namely grains, legumes, and dairy. As a result, it can lead to deficiencies of calcium and certain B vitamins. It can also be difficult to obtain sufficient fiber on this diet. While a handful of small studies have found that it is effective for short-term weight loss, there is no evidence for long-term results.

Plant-based diets. Even though vegetarians tend to weigh less than nonvegetarians, health experts have had difficulty teasing out whether this is because of their diets or other healthy lifestyle factors. While more research is needed, a small study shed some light on the question. Researchers assigned 63 overweight volunteers to one of five different diets: nonvegetarian, semi-vegetarian (limited in red meat and poultry), pesco-vegetarian (vegetarian with fish), vegetarian (plants plus eggs and dairy), or vegan (plants only). After six months, those who followed the vegan diet achieved the greatest weight-loss success, dropping 7.5% of their body weight, followed by vegetarians, with a 6.3% reduction in body weight.