The Top 10 Worst Weight-Loss Diets of 2021

The worst diets of the year include several popular weight-loss plans.

If you recently decided to try out a new diet, you're in good company. Every year, about 45 million Americans go on a diet, spending roughly $33 billion on weight-loss products, according to Boston Medical Center. But even the most popular diets don't necessarily guarantee success — and some may do more harm than good.

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Putting the latest diet fads to the test, U.S. News & World Report evaluated the top diets with the help of a panel of health experts. While the highest-ranked regimens are easy to follow, nutritious and safe for a large variety of people, the diets lowest on the list are much the opposite.

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For healthy weight loss in 2021, steer clear of these 10 worst diets.

10. GAPS Diet

While bananas are GAPS diet-approved, the diet website recommends only bananas with brown spots on the skin.
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The Gut and Psychology Syndrome Diet (aka GAPS) is based on establishing a link between your digestive system and brain, according to the GAPS website. Unlike other diets, the goal of this regimen is to help improve gut health through diet, supplements, detoxification and lifestyle changes.

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The GAPS Diet is new to U.S. News & World Report's list this year. But it's probably not one you want to test out. This strict elimination diet involves cutting grains, dairy, certain legumes and starchy vegetables, among some other nutritious foods, according to the diet's website. Such a drastic plan can set you up for nutritional deficiencies.

Plus, get this: There's no reliable research to show the GAPS diet can actually help improve gut health.

9. AIP Diet

The AIP diet focuses on eating organ meats but recommends grass-fed varieties.
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The Autoimmune Protocol Diet (also known as the Autoimmune Paleo Diet) is an extension of the paleo diet (more on that below) that aims to reduce inflammation and alleviate autoimmune disorder symptoms, according to U.S. News & World Report.

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The goal of the AIP Diet is to help pinpoint food allergies and intolerances by eliminating a variety of foods, including nightshade vegetables (eggplant, tomato), grains, dairy, eggs, legumes, nuts and seeds. Instead, the regimen focuses on organ meats, bone broth and fermented foods and oils.

Because the diet involves strict elimination, weight loss can be a byproduct, though it's far from the best way to go about shedding pounds. The real goal of the diet is to pinpoint intolerances and allergies, but you should talk to your doctor or a dietitian before trying it for that reason.

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8. Acid Alkaline Diet

Nuts are an Acid Alkaline Diet-approved food.
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The Acid Alkaline Diet suggests that eating acid-forming foods, like beef, can throw your pH levels out of balance, resulting in poor overall health, according to U.S. News & World Report. As we're constantly putting acidic foods in our systems, our bodies are too preoccupied with removing the acidity to support good health, the diet suggests.

The eating regimen for the Alkaline Diet is especially challenging, as it requires you choose foods that are either neutral or alkaline (7 to 14 on the pH scale). Generally, this involves eliminating meat, poultry, dairy and grains, focusing instead on healthy fats, fruits, vegetables and legumes.

7. Whole30 Diet

The founders of the Whole30 diet believe that many mental and physical health issues are caused by our diets.

The Whole30 diet claims to help eliminate cravings, improve energy and sleep and promote weight loss, according to the Whole30 website. This diet involves eliminating added sugar, alcohol, grains, legumes, dairy, sulfites and baked goods for 30 days. Then, after the 30 days are up, participants can reintroduce certain food groups slowly, with the goal of identifying which foods make them feel better or worse.

Although the Whole30 diet isn't particularly unsafe, it is restrictive and requires high levels of commitment to actually "work," according to U.S. News & World Report. Closely following Whole30 requires daily planning and meal preparation in order to successfully identify which foods do and don't work for your body, and that level of commitment is too much for a lot of people.

6. Fertility Diet

The Fertility Diet recommends full-fat dairy products.
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As it sounds, the goal of the Fertility Diet is to promote overall reproductive health, according to U.S. News & World Report. By increasing consumption of healthy fats, whole grains and plant protein, while limiting refined carbs and red meats, the Fertility Diet suggests that women can improve their chances of getting pregnant.

Weight loss may sometimes be a byproduct of the diet, as it's mostly lower-carb. But while this diet is pretty easy to follow and encourages a generally healthy eating plan, there's no evidence to suggest it can actually improve your fertility or ability to get pregnant, per U.S. News.

Did you know that keeping a food diary is one of the most effective ways to manage your weight? Download the MyPlate app to easily track calories, stay focused and achieve your goals!

5. Dukan Diet

This diet promises you’ll lose up to 10 pounds in the first week.

The Dukan diet focuses on protein intake, rather than counting calories, as the key to weight loss, according to U.S. News & World Report. Like Atkins and keto, this diet is based on the idea that cutting carbs forces your body to burn fat. However, unlike other low-carb regimens, Dukan focuses more on increasing protein consumption.

The Dukan diet can lead to short-term weight loss, but it's an extremely restrictive regimen. While you can eat an unrestricted amount of protein and veggies, all other food groups are either curtailed or cut completely. U.S. News panelists warn that the diet can lead to nutritional deficiencies.

4. Glycemic-Index Diet

Leafy greens are on the lower end of the glycemic index.
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Whereas the Acid Alkaline Diet (see #8 on the list) recommends eating according to pH level, the Glycemic-Index Diet encourages choosing foods based on your blood sugar levels, according to the Mayo Clinic.

The glycemic index is a scale that ranks carbohydrate-rich foods according to their effect on blood sugar levels, per the Mayo Clinic. So, the goal of the Glycemic-Index Diet is to prioritize carbs that are less likely to cause blood sugar spikes.

As with most of the diets on this list, weight loss can be a byproduct of this regimen, considering it involves cutting many high-sugar foods, according to the Mayo Clinic. However, there are plenty of healthy fruits (like watermelon and banana) that are technically on the higher end of the glycemic index scale.

Also, considering the diet doesn't actually take calories into account, there's no promise you'll actually lose weight on the plan.

3. Paleo Diet

If cavemen didn’t eat it, it's not included in the paleo diet.

You've probably heard of the paleo diet, given that it's one of the most popular diets right now. It's based on the idea that you should eat only foods that the cavemen had available. Refined sugars, grains, dairy and legumes are off the table, while meat, fish, fruits and vegetables are all fair game.

Though this diet does emphasize a whole foods-based eating regimen, it can quickly become pricey and restricts grain consumption. Whole grains, especially, are part of a healthy diet and may help reduce the risk of heart disease, stroke and diabetes, according to the American Heart Association.

2. Anti-Inflammatory Diet

Salmon is high in omega-3 fatty acids, which are approved on this diet.
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While most diets have a specific list of dos and dont's, the Anti-Inflammatory Diet is a little more general. The goal of the diet is to, simply, lower inflammation in the body, which has been linked to various health conditions, according to U.S. News & World Report.

This eating style is rooted in the idea that what you eat is directly related to inflammation levels. So, by eating a diet rich in fish, healthy fats, fruits and vegetables, the Anti-Inflammatory Diet suggests you can lower your body's inflammation, ultimately helping promote better overall health and weight loss, per the above-mentioned report.

While this may be a healthy eating pattern, there's little evidence that reducing inflammation induces weight loss.

1. Fast Diet

The Fast Diet requires you to eat regularly for five days, then cut your calories down to 20 percent of your normal intake for two days.

What if we told you there's a weight-loss diet out there that lets you eat whatever you want? The Fast Diet allows you to do just that — as long as you significantly cut calories two days a week, according to U.S. News & World Report.

For five days a week, you consume your typical daily calories. Then, for two nonconsecutive "fast" days, you restrict to either 600 calories for men or 500 calories for women.

While this diet does have few rules to follow and only involves two days of dieting, the extreme calorie restriction can be unsafe and will likely leave your stomach grumbling.

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