Is Intermittent Fasting a Diet Craze or Legit Health Regimen?

Is fasting and calorie restriction a safe way to maintain a healthy weight? We decode the research to find out.

“Oh, not for me, thank you; it’s fast day.” You may have heard this phrase lately, and you’ll hear it more often if the “fast diet” trend continues to grow. Most of the claims around fast diets, or intermittent fasting, are varied and impressive in terms of weight loss and preventive health benefits.

What is it?

The fast diet craze began in the UK in 2012 after medical doctor-turned-journalist Michael Mosley released the BBC documentary titled Eat, Fast and Live Longer. He subsequently wrote the book The Fast Diet (Atria Books, 2013).

This type of eating plan can be carried out in many different ways, such as calorie restriction, intermittent fasting, or alternate day fasting (see sidebar on page 63). All drastically reduce our calorie intake. Mosley’s 5:2 method allows people to eat normally for five days a week, then restricts calorie intake to 500 for women and 600 for men on two or more nonconsecutive days per week. The amount and pace of weight loss will depend on your starting weight.

What to expect

Krista Varady, PhD, is associate professor of kinesiology and nutrition at the University of Illinois. She’s the author of The Every Other Day Diet (Hyperion, 2013) and is behind some of the preliminary human research on the effects of alternate day fasting (ADF). “Most people lose 10 to 30 pounds in eight to 12 weeks by ADF,” she says.

“Larger people lose more per week compared to smaller people … but normal weight people can use ADF to lose the last five to 10 pounds,” she says.

Mosley claims that with his 5:2 method, weight loss is roughly 1 lb (0.5 kg) per week for women and slightly more for men.

Other health benefits

Aside from weight loss, Varady says, “The most notable health benefits of ADF include decreased abdominal fat, LDL cholesterol, triglycerides, glucose, insulin, and blood pressure.”

Study results

In a 2013 study of normal and overweight individuals who followed ADF for eight to 12 weeks, participants experienced a 20 to 25 percent decrease in triglycerides.

Some studies involving daily restriction to 600 calories have shown a normalization of fasting plasma glucose levels in those with type 2 diabetes, improvement of pancreatic function, and reduction of triglycerides.

A 2013 review found that intermittent fasting is easier to stick to than traditional calorie control methods of weight loss.

Intermittent fasting causes a positive impact on the metabolic syndromes associated with heart disease. It may be an easy, cost-effective preventive measure for many people.

A 2013 review in the British Journal of Diabetes and Vascular Disease found that a daily restriction of 600 calories may be too severe for many type 2 diabetes patients, but an intermittent fasting strategy may help improve metabolic parameters and insulin levels and sensitivity, as well as prevent diabetic complications.

The main concern many people have is that they’ll end up bingeing on non-fast days. This is not so, according to Varady. “Most people don’t binge eat during ADF. They only eat 10 percent more than they usually do on the feast day,” she says, although she does stress this has not yet been proven with the 5:2 method. Side effects may include headaches, bad breath, and fatigue within the first two weeks, but these tend to subside within 10 to 14 days.

If you have a medical condition or health concern, consult your health care practitioner before beginning this or any other type of calorie restriction plan or intermittent fasting.

How to restrict calories

Restricting our calorie intake so dramatically is going to feel like a daunting prospect at first. Like most things, the first week will be the hardest to get through. Here are some tips for success.


Not only does water have zero calories, but also continually sipping throughout the day can make you feel fuller and distract you from troublesome tummy rumbles. Try to drink a glass of water before eating a meal to help you feel satisfied.


Don’t wait until the night before a fast day to plan what to eat. Keep fast-friendly fodder in the fridge so you can pack a lunch and some snacks in advance. If you find yourself frantically rummaging in cupboards five minutes before you leave the house, you’re more likely to cheat.

Use an app for that

If you’re a smartphone junkie, there are a myriad of diet and fitness apps to help you with calorie counting. Five hundred to 600 calories is a lot different than your regular day, and some foods may surprise you with the amount of calories they pack in. An app is a handy way to check on how you’re doing throughout the day. It’s also a great tool to help plan your meals ahead of time.

Work out gently

You’ll probably experience some fatigue on your fast days. It’s suggested you take your workouts down a notch, and try to limit high-endurance activities.

How to stay full

Toss a big salad

Salads are a great way to trick yourself into thinking you’ve had a big meal, purely because they take a long time to eat. For example, three cups of raw spinach contain just 21 calories, and yet your plate will be piled high. Try teaming it with crunchy raw vegetables such as cucumber, celery, and peppers.

Add lean protein

Good proteins to choose are eggs, fish, and poultry. These will give you an energy boost without breaking the calorie bank. Added oils will increase your calorie count significantly, so try to steam, boil, and grill.

Substitute healthy carbs

One cup of bean sprouts has 31 calories, as opposed to a cup of calorific noodles at 221 calories. Grated and steamed cauliflower is a tasty substitute for rice. This savvy swap will save you 95 calories per cup.

Types of calorie restriction plans

Calorie restriction

This classic method of cutting back on daily calorie consumption is in line with the old rule of thumb that if we burn off more calories than we take in, we’ll lose weight.

Intermittent fasting

This broad term covers the different types of diet plans that involve eating normally some of the time and drastically cutting back calories at other times. It could describe the 5:2 diet, alternate day fasting, or other practices such as Ramadan.

Alternate day fasting

Researched by Krista Varady, ADF involves eating normally every second day and restricting calorie consumption to 500 on every other day.


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