Fast Diet

What is The Fast Diet?

The Fast Diet is a low-calorie plan that aims to help followers lose weight – specifically fat – and reduce their risk of a host of chronic diseases by severely limiting calories two days a week. The plan – created by Michael Mosley, a journalist trained as a doctor at the Royal Free Hospital in London, and Mimi Spencer, a journalist and author – mirrors a pattern of eating often referred to as the 5:2 diet: you eat normally for five days of the week and cut your calories to about 25% of normal intake on two non-consecutive days of the week. Men consume just 600 calories on their two weekly fast days, while women are limited to 500 calories. Those calories should be spent wisely on high-protein foods, such as skinless chicken, nuts and legumes, as well as fruits and veggies with low glycemic loads like strawberries and carrots.

On the other five days of the week, there’s no calorie cap, and no food is off-limits. This freedom isn’t permission to binge and make up for your two fast days, but it does mean you shouldn’t feel guilty about eating a slice of cake. U.S. News experts evaluate the Fast Diet poorly in all rankings, mostly due to its tough-to-follow nature and health risks in some populations.

Pros & Cons

Few rules to keep track of
You’re only dieting two days of the week

Unsafe for some people
You may get hungry

The Fast Diet ranked #30 in Best Diets Overall.

How does The Fast Diet work?

Choose two days each week – make sure they’re not in a row – to fast. Then, plan to savor your calories on those days by following these tips:

Aim for 50 grams of healthy protein from sources like steamed white fish, skinless chicken, tofu, nuts, seeds, legumes and eggs.
Round out your meal, meals or snacks with low-calorie, fiber-rich and nutrient-dense fruits and vegetables.
Plan when you consume your calories based on what’s most appealing and sustainable to you – whether that’s a single 500- or 600-calorie meal or several hundred-calorie snacks.

For more guidance, look to “The Fast Diet” book, which was most recently updated in 2015 and includes the authors’ experiences with the plan.

How much does The Fast Diet cost?

Cost isn’t really a factor for the Fast Diet, given that you’re eating normally most days. There’s a good chance you’ll wind up buying fewer foods on fast days and thus spend less on your grocery bills. But keep in mind that if you follow the diet authors’ advice and get your calories from high-quality foods, they can be a bit pricier than cheap, high-calorie fast-food cheeseburgers.

Will The Fast Diet help you lose weight?

You’ll probably lose weight on the Fast Diet because you’ll consume significantly fewer calories than you normally would on two days of the week. If you actually stick with the plan, you’ll steadily drop weight. And because the two fast days are nonconsecutive and allow for at least some eating, the diet authors have found that people don’t typically binge and overeat on the nonfasting days.

A 2016 meta-analysis published in Obesity Science & Practice found that alternate-day fasting is an effective dietary method and may be superior to very-low-calorie dieting for some patients.
A 2013 study in the journal Metabolism found that obese people who alternated days of fasting with either high-fat or low-fat diets lost weight and inches from their waist and reduced some heart disease risk factors.
In a 2011 study published by the American Association for Cancer Research, researchers at Genesis Prevention Center at University Hospital in South Manchester, England tested the effects of three kinds of diets on 115 women. One diet looked like the Fast Diet (five days of normal eating and two days following a calorie-restricted, low-carb diet each week), another restricted carbs two days a week but had no calorie restrictions and a final group followed a calorie-restricted Mediterranean diet for all seven days of the week. After four months, participants following the intermittent low-carbohydrate diets lost an average of 9 pounds, while those on the Mediterranean diet lost an average of 5 pounds.
In a randomized trial of 107 overweight or obese premenopausal women, researchers found that participants who followed an intermittent food energy restriction plan (25% restriction two days a week) lost a comparable amount of weight to the participants who followed a continuous energy restriction plan. After six months, participants following the intermittent calorie restriction plan lost an average of 14 pounds each. Results were published in 2011 in the International Journal of Obesity.
A study published in the July 2013 issue of Physiology & Behavior doesn’t discuss intermittent-day fasting, but it addresses the concern of overeating after fasting. Researchers at Cornell University either fed breakfast to or withheld breakfast from a group of student volunteers. They found that those who skipped breakfast reported being hungrier than those who ate breakfast. They also ate more at lunch. Still, the amount they ate didn’t fully compensate for the missed meal. Volunteers who skipped breakfast consumed 408 fewer calories over the course of the day than those who ate breakfast.
Studies on every-other-day fasting show mixed results. One published in 2010 in the Nutrition Journal suggested that the technique was effective among a group of obese patients. A group of 16 participants ate only one meal – lunch – every other day, and they were limited to about 500 calories. That’s the same amount of calories women consume on the Fast Diet’s fasting days. On the days when the study participants were not fasting, they were not constrained to any rules. Over the course of eight weeks, the participants lost an average of 12 3/10 pounds.

How easy is The Fast Diet to follow?

The Fast Diet is ranked #21 in the Easiest Diets to Follow

The Fast Diet is easy to follow – on five days a week, when it’s not a diet at all. Drastically cutting your calories on fast days, however, will likely be a challenge.

The Fast Diet is pretty convenient: The Fast Diet’s minimalist set-up makes it fairly convenient, given you can count calories (or use an app like My Fitness Pal) and restrain yourself. The biggest inconvenience is likely the very premise of the diet – ignoring hunger and consuming few calories on two days of the week.

You can find plenty of low-calorie, Fast-friendly recipes. “The Fast Diet,” “The Fast Diet Cookbook,” “The Fast Days Cookbook” and “The Fast Beach Diet” as well as the “The 8-Week Blood Sugar Diet Cookbook” and “The Clever Gut Diet Cookbook,” include numerous recipes and meal plans for 500- and 600-calorie fast days.

You can eat out restriction-free five days a week on the Fast Diet. On fast days, however, the inflated portions at many restaurants may be a challenge, given that one serving of fries could possibly add up to your whole day’s worth of calories. Choosing restaurants with disclosed calorie counts may take some guesswork out of ordering. Be prepared to stick to the diet plan while other friends are ordering freely.

Alcohol is a fair game most days of the week on the Fast Diet. On fast days, however, your calories are so precious that it’s better to spend them on foods with nutritional value. So steer clear of alcohol on these days.

How much should you exercise on The Fast Diet?

The Fast Diet is only an eating pattern, but that doesn’t mean you shouldn’t exercise. In fact, being physically active lowers your risk of heart disease and diabetes, helps keep weight off, and increases your energy level. Most experts suggest getting at least 30 minutes of moderate-intensity exercise – like brisk walking – most or all days of the week.