What Is the Flat Belly Diet? A Detailed Beginner’s Guide

Developed by Cynthia Sass, a registered dietitian and a nutrition and wellness consultant, and former Prevention magazine editor Liz Vaccariello, the Flat Belly Diet claims to be able to help you lose up to 15 pounds in 32 days.

The diet is based on the theory that monounsaturated fatty acids, or MUFAs, target and destroy belly fat, while promoting fullness and preventing overeating.

The regimen loosely aligns with the Mediterranean diet, which emphasizes plant-based, whole foods, and promotes many of the same foods, including avocados, soybeans, whole grains, olive oil, dark chocolate, seeds and nuts. However, unlike the Mediterranean diet, the Flat Belly Diet relies on calorie restriction to achieve weight loss. It’s a 32-day program, which calls for consuming 1,600 calories per day, split across four meals.

• Planet friendly. The diet considers the environmental effects of food choices. It’s largely plant-based and/or the foods are mainly sustainably grown/produced.
• Vegan or vegetarian friendly. Recipes can be easily modified for a vegan or vegetarian diet.
• Gluten-free friendly. Recipes can be easily modified and still follow a gluten-free diet.
• Halal friendly. Recipes can be easily modified and still follow a halal diet.
• Kosher friendly. Recipes can be easily modified and still follow a kosher diet.

Although there’s no recent research on the Flat Belly Diet and weight loss, you’ll likely lose weight on the diet simply due to the calorie restriction, says Lauren Sepe, a clinical nutritionist and in-house nutritionist at Kellman Wellness Center, a functional and conventional medical practice, in New York City.

Since many people consume about 2,000 calories or more per day, a 400 to 600 calorie deficit on the Flat Belly Diet is likely to result in weight loss.

The Mediterranean diet, which the Flat Belly Diet is loosely modeled after, seems to promote weight loss or a lower likelihood of being overweight or having obesity, but even if those benefits hold up, whether the same can be said of the Flat Belly Diet is unproven.

“If you have previously eaten an unhealthy diet, simply switching to a more healthful one including plenty of fruits and vegetables, healthy fats and primarily plant-based foods will likely result in weight loss,” Sepe says.

Short-Term Weight Loss

• In a small study commissioned by Prevention magazine and referenced in the foreword to the “Flat Belly Diet” book, researchers tracked nine overweight women who were following the Flat Belly Diet. After 28 days, participants lost an average of 8.4 pounds and 2 inches off their waist during the study period, as well as reduced visceral belly fat mass by an average of 33% (1).
• One small study of 11 people who were overweight showed that while high-carb diet plans increased harmful belly fat, high-fat diet plans did not, even when both types of plans provided the same number of calories (2).

Long-Term Weight Loss 

Currently, there are no studies that link the Flat Belly Diet with long-term weight loss. However, research on the Mediterranean diet may be helpful.

• A study of over 32,000 people over 12 years showed that adherence to the Mediterranean diet was associated with less weight gain and smaller changes in waist circumference for people who were within a normal weight range at baseline (3).

Weight Maintenance and Management

In general, eating more plant-based foods can improve overall health. Studies show that plant-based eating is associated with a reduced risk of chronic disease and obesity.

“The Flat Belly Diet,” an essential guidebook, is $15.99. Additional books range from $7.99 (“Flat Belly Diet! Pocket Guide”) to $26.99 (“Flat Belly Diet! Family Cookbook”).

What Costs Are Related to the Flat Belly Diet?

Some ingredients you need for the diet – like high-quality extra-virgin olive oil, fresh produce, avocados, nuts and seeds – may be on the higher price end. However, this is generally an affordable eating program, Sepe says.

While some of the foods on the Flat Belly Diet may be a little pricey, you can try these tips to eat healthy on a budget:

• Try buying produce from your local farmers’ market, where prices directly from the grower might be lower and the fruits and vegetables could be fresher.
• Meal planning and prep can save money by letting you prepare foods that can be eaten throughout the week.
• Shop around for olive oils, you can probably find high-quality, moderately-priced options.
• Do the program with a friend, buy foods together and share meal prep.
• Buy nuts, seeds and other items in bulk.

This diet is fairly easy to follow, experts say.

“It is not overly strict with the foods you cannot eat and can be adapted for many different diet options, such as vegetarian, vegan and so on,” Sepe says.

However, the Flat Belly Diet may be difficult to sustain in the long run because of its caloric restrictions. The concept of controlling calorie consumption to no more than 1,600 calories per day is not an effective method of long-term weight management and loss.

The Flat Belly Diet is not recommended for people under age 18, anyone who is pregnant or breastfeeding or anyone with an eating disorder, as it promotes calorie counting and food restriction, Sepe says.

Buying the book is a good place to start.

“Flat Belly Diet! Family Cookbook” and “Flat Belly Diet! Cookbook” are packed with breakfast, lunch, dinner, dessert and snack recipes. Choices range from crab primavera with spaghetti to sweet-and-sour blueberry parfaits. All recipes include information on calories, protein, carbohydrates, fat, saturated fat, cholesterol, sodium and fiber.

Pantry Edit

You’ll want to keep some staples in your pantry, including high-quality extra virgin olive oil, seeds, nuts and gluten-free grains, like quinoa, Sepe says.

Start a Food Diary

Food diaries are a helpful way to track what you’re eating.

“It makes you more mindful of your food choices and helps you track exactly what you’re eating,” Sepe says. “Be sure to include everything you eat and drink, even if you eat something you are technically not supposed to have. It’s a good way to keep yourself accountable.”