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The Best Diets For Weight Loss, Ranked: How Keto, Vegan, IF, The Mediterranean Diet & More Stack Up

Vincent M. Pedre, M.D.
Board-Certified Internist
By Vincent M. Pedre, M.D.
Board-Certified Internist
Dr. Vincent M. Pedre is a board-certified internist in private practice in New York City since 2004. He serves as medical director of Pedre Integrative Health, president of Dr. Pedre Wellness, and is the author of Happy Gut.
Illustration by Megan Doty / mbg Creative
January 9, 2019

If I got paid every time someone asked me about a particular diet's merits or drawbacks, I could comfortably retire right now on some remote Tahitian island.

As a medical doctor who specializes in functional medicine and gut health, I consistently see how dysbiosis (or gut imbalances) can sabotage fat loss. Simply put: If you want to lose weight, start with your gut. Your gut microbiome dictates how you absorb and process calories, even affecting your fat storage and basal metabolic rate. 

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When I critique a particular plan for weight loss, I take an approach that also incorporates gut rebalancing, because the two factors are synonymous. From that perspective, most plans don't pass. They include foods that contain gluten, added sugar, artificial sweeteners, and other food sensitivities.

Besides, no diet is one-size-fits-all. Some people thrive eating a ketogenic-based diet, whereas for others a few days on that plan will leave them bolting for the nearest bagel. Here, I've examined the pros and cons of six popular diets. My evaluation includes whether the plan will help you lose weight and support gut health.

To do that, I've combined my own experience working with thousands of patients along with extensive research about each plan. Here's how they pan out.

Low-Carb Diets

Carbs have unfairly become synonymous with weight gain. After all, ice cream and cauliflower are both carbohydrates. One is healthy; the other, not so much.

A low-carbohydrate diet is usually moderate to high in fat and/or protein. How low you need to go with carbohydrates to get weight loss results depends. I've had patients go as high as 100 grams a day (still pretty low-carb compared with regular diets) and lose weight. Others need to dip low: 20 or 30 grams.

That still allows a good many gut-supporting plant foods including leafy and cruciferous veggies, low-sugar fruits, nuts, and seeds.

Research shows that low-carb can help you lose weight and keep it off. One review of 10 clinical trials (that spanned from three to 24 months) found the Atkins diet could create "clinically meaningful short-term weight loss." Six of the eight long-term reviews also found this diet effective for long-term weight loss.

In fact, of all the current popular diets in one systematic review, the Atkins diet had the most evidence to create short-term and long-term weight loss. I wrote extensively about low-carb diets in this blog.

Pros: Low-sugar intake means you keep your blood sugar and insulin levels steady, supporting weight loss and steady energy. While somewhat restrictive, patients overall find they feel full and satisfied eating healthy low-carb foods.

Cons: Overconsuming meat and other animal foods neglects gut-supporting plant foods. You want to work in some quality carbs. Food sensitivities like gluten can also slip into low-carb plans. Some Atkins packaged foods, for instance, contain soy, dairy, artificial sweeteners, and other problematic ingredients.

Paleo Diets

This popular diet mimics what our hunter-gatherer ancestors ate, emphasizing whole, unprocessed foods. These are the foods your great-grandparents ate and recognized, not the ubiquitous Frankenfoods that oftentimes pass as "diet food" today. There is no one definition of paleo diets, although for weight loss you would want to minimize higher-sugar fruits like bananas (which technically would be paleo).

One short- and one long-term clinical trial found that the Paleolithic diet created an average weight loss of 9 percent after six months and 10.6 percent after 12 months.

Pros: Many of these foods are rich in nutrients and low in sugar, supporting healthy weight loss. Our paleo ancestors ate way more fiber than we do today, supporting satiety and a diverse gut microbiome, which is synonymous with health.

Cons: As with low-carb, overemphasizing meat can mean you're not getting enough plant foods. Our hunter-gatherer ancestors ate plenty of leafy greens, fruit, and other foods rich in fiber and nutrients!

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Vegan and Vegetarian Diets

A vegan diet eschews all animal foods. For some people, that includes anything an animal created (such as honey). Vegetarian diets, on the other hand, allow some animal foods, including eggs and dairy. With the right plan, vegan and vegetarian diets can help you lose weight. The Ornish diet, which is plant-based, created an average weight loss of approximately 2.9 percent after six months and 2.6 percent after 12 months.

Pros: Focusing on organic plant foods provides a rich array of nutrients that are also better for the planet. The nutrients and fiber in foods like leafy and cruciferous veggies, low-sugar fruits, nuts, and seeds are fabulous fuel for your gut while keeping you full for fewer calories.

The factory farm situation is nasty: Meats and other animal products are often pumped with hormones, antibiotics, and other junk. Never mind that many animals are fed grain, soy, and other problem foods that don't belong in their diets.

Cons: For people with insulin resistance or who are otherwise sensitive to carbohydrates, too many plant foods can stall fat loss. A vegan diet can also feel incredibly restrictive, especially if you travel a lot or otherwise can't prepare your own food.

Mediterranean Diet

While no one true definition exists, the Mediterranean diet is typically low in saturated fat and high in vegetable oils. U.S. News & World Report voted it (along with the DASH diet) as best overall diet. The diet gets impressive results. After 12 months, people lost an average of 8.7 percent. (When they went low-carbohydrate Mediterranean, that average weight loss increased to 10.3 percent.)

Pros: While not specially designed for weight loss, many staples on the Mediterranean diet can certainly help you lose weight. A diet rich in extra-virgin olive oil, vegetables including leafy greens, nuts, and wild-caught fish can support fat loss and a healthy gut.

Cons: For some people (including those who are insulin resistant), the Mediterranean diet—which also incorporates whole foods like fruit and legumes—can be too high in carbohydrates. Likewise, if you need specific instructions about what to eat and how much to eat, this plan can feel vague. The Mediterranean diet also unfairly demonizes saturated fat, which newer studies show can actually be healthy from foods like extra-virgin coconut oil and grass-fed beef.

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Ketogenic Diets

While individual tallies vary, many ketogenic plans include at least 55 to 60 percent dietary fat. Most other calories come from moderate protein intake along with very low amounts of carbohydrate. You literally retrain your body to utilize fat rather than sugar as fuel.

One problem I've seen among ketogenic diets is the inability to stick with the plan long term, but that depends. One review of randomized controlled trials found that over a year or more, low-carbohydrate diets (such as ketogenic diets) "led to significantly greater weight loss compared to low-fat interventions. BMR [Basal Metabolic Rate] dropped by more than 400 kcal/day on a low-fat diet when compared to a very low-carb diet."

Pros: Recent press shows keto diets can help you lose weight fast. I've talked extensively about this high-fat, low-carbohydrate diet here. You can eat satisfying foods going keto without ever feeling hungry.

Cons: You can easily rack up 4,000 or more calories daily eating these high-fat foods. Sure, you'll burn fat, but it will be dietary fat rather than body fat. Many ketogenic diets neglect fiber-rich plant foods that support your gut flora. And if your body can't tolerate large amounts of dietary fat (or the thought of eating that much fat makes you wince), a ketogenic diet isn't for you.

Intermittent Fasting

I've talked about the various styles of fasting here. Essentially, you alternate periods of eating with not eating (or fasting). How long you abstain from eating depends on your plan but usually entails anywhere from 16 to 24 hours or longer. While most research involves animals, one study among 51 obese men over 16 weeks found those who did intermittent fasting achieved greater weight and fat loss.

Pros: Fasting can complement many plans here and enhance your weight loss. Consistent fasting also gives your gut a break and allows your body to access fat for fuel. Fasting is free, requires no special products, and allows flexibility since you can do it nearly everywhere.

Cons: Hunger becomes the biggest obstacle for many people. Overeating or binge eating can become problems for some people. Certain demographics (including people with adrenal or thyroid issues) should consult with a functional practitioner before they undergo fasting.

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The best diets for weight loss, ranked.

Based on my research and empirical evidence, I've ranked these seven diets from best to worst based on their ability to help you lose weight and keep it off as well as support gut health:

  1. Intermittent fasting (fasting can complement any diet plan)
  2. Ketogenic diet (tied with intermittent fasting)
  3. Low-carb diet (bonus if you do a low-carb Mediterranean diet)
  4. Paleo diet
  5. Mediterranean diet
  6. Vegan/vegetarian diets
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From that criteria, I've found ketogenic diets combined with moderate fasting (around 16 to 18 hours a day) eliminates the drawbacks of both plans and optimizes fat loss. I've outlined the ideal plan, which I've called the Cyclitarian diet, here. (Vegans and vegetarians, you can adopt this plan easily.) Ultimately, what matters is what works for you that helps you lose weight, create gut balance, and maintain that success.

You can tweak nearly any plan here to accommodate all three goals. However, the most important thing is that a plan feels doable—if any of these plans feel like torture and you're counting the days till you can go off, that's probably not the best choice for you!

Vincent M. Pedre, M.D.
Vincent M. Pedre, M.D.

Vincent M. Pedre, M.D., medical director of Pedre Integrative Health and president of Dr. Pedre Wellness, is a board-certified internist in private practice in New York City since 2004. He completed his bachelor’s degree in Biology at Cornell University before attending the University of Miami School of Medicine and completed his residency in Internal Medicine at the Mount Sinai School of Medicine. He has appeared on the Martha Stewart Show and ABC and is the author of Happy Gut: The Cleansing Program to Help You Lose Weight, Gain Energy, and Eliminate Pain. Dr. Pedre is a clinical instructor in medicine at the Mount Sinai School of Medicine and is certified in yoga and medical acupuncture.

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