Fasting diets to lose weight

Intermittent Fasting

Alternate day fasting, the latest diet by James Johnson, has hit the weight loss world, but can intermittent fasting really help you to shift those pounds - and keep them off? Dietitian Juliette Kellow BSc RD investigates

When it comes to losing weight, the idea of dieting only every other day may seem like an attractive one. After all, knowing we can indulge in our favourites ‘tomorrow’ may make dieting seem more bearable.

But as is always the case with anything that sounds too good to be true, there’s a downside – and in this case, it’s eating very little on the days in between. Nevertheless, some scientists believe that alternate day fasting doesn’t just help us lose weight. It may also make us healthier, reducing our risk of health problems such as heart disease and cancer, and easing the symptoms of conditions such as asthma. Supporters of this fasting diet even say it can help us live longer.

One of the most popular diet books based on the idea of intermittent feasting and fasting is The Alternate-Day Diet, written by plastic surgeon Dr James Johnson. Here’s the lowdown…

What is The Alternate-Day Diet?

In a nutshell, this diet involves alternate day fasting, eating very little on one day followed by eating what you’d normally have the next day.

What’s the theory of intermittent fasting?

The idea that restricting our calories makes us healthier and increases our life expectancy has been around for decades and forms the basis for a book called The Longevity Diet by Brian Delaney and Lisa Walford. As far back as the 1930’s, an American scientist found that drastically reducing the calories fed to mice helped them to live longer and be healthier. In more recent times, the same thing has been shown in a variety of life forms including fruit flies, roundworms and monkeys.

The idea of severely restricting calories every other day – rather than every day – to improve health and life expectancy came in 2003 following laboratory research carried out at the 1National Institute on Ageing in America.

After 20 weeks, mice who were allowed to eat as much as they wanted on one day but not fed the next day, lived longer and had lower levels of glucose and insulin and improved insulin sensitivity compared to mice that were allowed to eat freely all of the time. But more importantly, these levels matched or were even better than those of mice who ate 40 percent fewer calories than normal every day. The scientists involved in the study concluded that alternate day fasting was just as likely to improve health and life expectancy as a daily calorie restriction.

Is there any evidence that the same thing happens in humans?

To date, most research has been carried out in laboratories with animals. There aren’t many human studies that have looked at the link between restricting calories and life expectancy – and even fewer that specifically look at the impact of alternate day fasting on health and longevity. Those human studies that have been carried out have generally had several limitations – namely that they include only a few participants and have only been carried out over a short period of time. It’s an area that needs a lot more research before any definite conclusions can be drawn.

So what’s the link with weight loss?

Unsurprisingly, restricting calories – whether it’s all of the time or fasting every other day – usually results in weight loss. The concept of an eating pattern that alternates between periods of fasting followed by periods of eating is sometimes known as Intermittent Fasting. When this pattern follows a 24-hour fast followed by a 24-hour feast, it’s sometimes called Alternate Day Fasting.

One small human study published in the 2American Journal of Clinical Nutrition has shown how alternate day fasting can aid weight loss. In this study, 16 normal weight adults followed an alternate day fasting regime for three weeks. On fasting days they had nothing but calorie-free drinks whilst on feasting days they were allowed to eat whatever they wanted. At the end of the study, the adults had: