What the science says about every popular diet

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What you do: The South Beach diet is a three-phase program designed by cardiologist Arthur Agatston in 2003. In the first phase, you cut out all carbs, fruits, and alcohol. In phases two and three, you gradually add some of those foods back in (as far as carbs go, you’re only supposed to eat whole-grain ones). It’s important to note that this is a commercial diet, so you may have to buy the official plan and materials.

What the science says: The diet focuses on whole foods, which is good since studies have shown this is the best approach for weight loss. Cutting out any of the food groups could leave you lacking nutrients, though. Some people on the diet have reported ketoacidosis, a condition with symptoms including bad breath, dry mouth, tiredness, dizziness, insomnia, nausea, and constipation. Studies have found South Beach diets (or those very similar to the name-brand version) could help people lose weight in the short-term, but researchers haven’t followed people long-term to see if it helps them keep the weight off. The problem here is that while the second two phases of the diet are somewhat reasonable, the first phase is very restrictive, so some people might have trouble sticking to it.

What you do: On the new Weight Watchers (the one Oprah has advertised lets you eat bread), their SmartPoints program assigns foods points based on their nutritional values. You get a set number of points per day depending on your height, weight, activity level, and how many pounds you want to lose. The plan can cost between about $20 and $70 a month, depending on whether you pay for add-ons like coaching or meetings.

What you do: There are many different kinds of vegetarians, but generally, you don’t eat meat or fish.

What the science says: In observational studies, vegetarians tend to weigh less than their carnivorous counterparts. Cutting meat from your diet could reduce your environmental impact as well, research has found. You have to make sure you get enough nutrients (especially protein) from other sources like nuts, grains, and dairy, though. But the benefits could be considerable: Studies have found that vegetarianism is linked with lower chances of heart disease and cancers, and higher chances of living longer.

What you do: Vegans don’t eat meat, fish, or dairy products — basically anything that came from an animal.

What the science says: Studies have found veganism has many of the same benefits as vegetarianism, including lowered risk for heart disease and cancer. Vegans also tend not to be obese, have high blood pressure, or get type 2 diabetes. Since you’re cutting many more foods from your diet, however, you have to be extra vigilant to get all the nutrients you need.

What you do: Only eat foods that aren’t heated above 115 degrees Fahrenheit. That means you can’t have pasta, most meats, pasteurized dairy products, or processed foods. It’s like a cold vegan diet.

What the science says: Raw food eaters get a ton of fruits and vegetables, which researchers have repeatedly found is beneficial. But the raw food diet cuts out a lot of food groups, meaning you could miss out on the essential nutrients your body needs if you don’t actively try to get them all from what you can eat. It can also be a lot of work to prepare and transform raw ingredients into desirable, edible foods. Studies have found people on the raw food diet do lose weight — namely because they’re eating less food — but that they tended to lack key nutrients like Vitamin A.

What you do: There are several versions of low-carb diets out there, but they all prescribe you eat less (or no) carbs. You typically replace these processed, sugary carbohydrates with fruits, vegetables, and meat. These diets also often have phases that start out more strict and gradually taper off over time so your body allegedly stops “craving” carbs.

What you do: The Dietary Approaches to Stop Hypertension (DASH) plan is designed to lower your blood pressure. You cut your sodium intake, switching from the sugary foods and red meats that so many Americans eat to whole grains, lean protein, and produce.

What you do: Avoid all grains, including bread, cereal, wheat, barley, and rye. Celiacs have an immune reaction when they eat gluten (the protein found in grains) that can cause diarrhea, tiredness, weight loss, bloating, anemia, and possibly serious complications over time if they don’t cut it out of their diets.

What you do: On the FAST diet, you eat normally for five days of the week, and then drastically reduce your calorie intake (500 a day for women, 600 for men) on the other two days. It’s a method known as “intermittent fasting.”

What the science says: Researchers have found that intermittently fasting mice tend to live longer, lose weight, and have fewer diseases, but they haven’t conducted the rigorous, long-term studies necessary to draw the same kinds of conclusions for humans. Fasting can result in headaches, dizziness, difficulty concentrating, and irritability (a.k.a. feeling “hangry“). Restricting your calorie intake drastically for only two days may be easier to maintain than doing it moderately all the time, but you have to be careful not to overeat on your five regular days. A small, six-month study found women lost a similar amount of weight on a 5:2 diet as on one that restricted their calories all seven days of the week. If you try this diet, the important thing to remember is to keep making healthy choices — no matter how many calories you’re eating.

What you do: Swear off dairy, grains, legumes, soy, alcohol, sugar, and processed foods for 30 days straight. You don’t have to count calories or weigh yourself.

What the science says: Restrictive diets can be much harder to follow, and Whole 30 is a very restrictive diet. It’s also a short-term plan, not the type of long-term lifestyle change that typically yields better results over time. Whole 30 is somewhat similar to the Paleo diet, which has only shown modest short-term effects in studies. Scientists haven’t studied Whole 30 specifically yet. But Dr. , the founding director of the Yale-Griffin Prevention Research Center, told Business Insider last summer that he was skeptical of the benefits people rave about on Instagram. “The grouping [of banned foods] is both random, and rather bizarre from a nutrition perspective,” he said. “If the idea is good nutrition, cutting out whole grains and legumes is at odds with a boatload of evidence.”

What you do: Eat foods like fruits, vegetables, nuts, and tofu to maintain your body’s natural slightly alkaline pH levels around 7.4. Avoid acidic foods like meat, sugar, dairy, alcohol, caffeine, and processed foods that could lower your pH. Strict adherence requires 80% of what you eat comes from alkalizing foods, with only 20% coming from acid-forming foods.

What you do: Eat only a specified food or juices for a certain amount of time. Cleanses can also go by the name “detox,” and celebrities often swear by them. Hopefully I don’t have to remind you that celebrities are generally not scientists.

But many popular diets aren’t based on sound scientific principles. Here’s what the science says about 15 popular diets, so you can decide which one — if any — might be right for you.