5 Diets That Actually Work (and 3 That Definitely Don't), According to Nutritionists (2025)

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Published Jan 24, 2018

5 Crash Diets You Should Never, Ever Try

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Best: The Mediterranean Diet

“The Mediterranean diet is based primarilyon wholeplant-based foods, including vegetables and fruit, as well as whole grains, legumes and nuts, with small amounts of animal products (primarily seafood). Butter is replaced withheart-healthyolive oil, red meat is limited to no more than a few times a month, eating meals with family and friends is encouraged and wine is allowed (in moderation). Studies suggest that this style of eating improves cardiovascularhealth and is associated with a reduced risk of cardiovascular death, certain cancers, certain chronic diseases and overall mortality. Extra bonus? It’s also easy to eat this way at many restaurants.” – Maria Marlowe, Integrative Nutrition Health Coach and author of "The Real Food Grocery Guide"

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Worst: The Fruitarian Diet

“Any diet that focuses on one food or food group (such as Fruitarian diet) is not good. No matter how nutritious a single food or food group is, our body needs a variety of nutrients for good health. In such a diet, it would be hard to get enough essential nutrients like B12, essential fatty acids like omega-3,iron and protein. And a lack of these nutrients can lead to a variety of problems, such as lethargy, anemia and decreased immune function. While these types of restrictive diets may help you lose weight in the short term, in the long run they’re unhealthy.” – Maria Marlowe

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Best: The Flexitarian Diet

“A blend of the words ‘flexible’ and ‘vegetarian,’ this diet does just that—it allows for flexibility with your approach to vegetarianism. The diet encourages people to follow a mostly plant-based dietbut does not eliminate meat products entirely (instead, it aims to reduce meat and saturated fat intake). It's a great way to eat more fruits, vegetables, nuts and legumes, which are important for overall heart health, and also provides a more realistic approach for long-term success.” – Melissa Buczek Kelly, RD, CDN

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Best: Plant-based Paleo (aka Pegan)

“Similar to the Mediterranean diet in its emphasis on fresh over processed foods, plant-based paleo takes it a step further by eliminating dairy, gluten, refined sugar and vegetable oils. While straight paleo also eliminates grains and beans/legumes, this version allows them in small amounts. Reframing how you looks at meat (not as the main dish but as a condiment or side dish instead), eliminating highly processed and refined foods, and putting the emphasis on veggies as the star of the plate can help lower our risk of heart disease and many chronic illnesses. It also aids in weight loss and maintaining a healthy body weight over the long run.” – Maria Marlowe

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Worst: The Hcg Diet

“Any diet that severely restricts calories or requires the addition of hormones [the HCG Diet involves injections of human chorionic gonadotropin] is not a healthy diet. The extremely low-calorie goal (500 per day) can cause the resting metabolic rate to slow and make it extremely difficult for people to maintain weight loss.”– Katharine Kissane, MS, RD, CSSD

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Best: The Dash Diet

“The DASH diet has been well researched and proven to lower blood pressure and cholesterol. This diet approach is very similar to the Mediterranean diet, with a focus on fruits, vegetables, whole grains, lean protein and low-fat dairy. Fatty meats, full-fat dairy and foods high in sugar and sodium are limited. I’ll often recommend this diet to my clients with high blood pressure or those who need to lower their cholesterol.” – Katharine Kissane

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Best: The Nordic Diet

“The Nordic diet also has some research regarding health benefits including lowering inflammation and risk for heart disease. It emphasizes the intake of fish (high in omega-3 fatty acids), whole-grain cereals, fruits (especially berries) and vegetables. Similar to the Mediterranean diet, the Nordic diet limits processed foods, sweets and red meat. This diet also emphasizes local, seasonal foods that can be obtained from Nordic regions. Of course, finding local Nordic foods may not be feasible for everyone, but I like the idea of eating more local foods and using what’s available from our natural landscapes.” – Katharine Kissane

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Worst: Tapeworm Diet

“It sounds crazy, but some people are intentionally swallowing a parasite (in the form of a tapeworm egg in a capsule) in the hopes of dropping pounds. This is an absolutely terrible idea and can have so many negative side effects, from diarrhea and nausea to headaches and general weakness. What's more, the worm can move to other parts of your body and attach itself to other organs, causing even more problems. Do not attempt!” – Maria Marlowe