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Is alternate day fasting good for your health?

WebMD Feature
Medically Reviewed by Dr Rob Hicks

Fasting doesn't seem like fun. It conjures up images of supermodels who exist on salad and diet drinks just to keep their size zero figures or maybe those drastic dieters who leave it to the last minute and need to lose half a stone before a wedding in a week's time!

It seems pretty extreme and there's always the concern you'll just put the weight back on when you stop, that's if you have the will-power to start in the first place!

The recent buzz has been alternate day fasting or intermittent fasting. There's some evidence that short periods of fasting could not only be a way to lose weight but also be potentially good for your health.

Do you lose weight fasting?

The simple answer is yes. It may not be the most practical - or safest - diet, though. Some people also use fasting as a way to cleanse the body of toxins, although experts say our bodies are perfectly equipped with organs that already do the job.

When you fast, your body is forced to dip into energy stores to get the fuel it needs to keep going, so you will definitely lose weight.

The big question is how long you will keep that weight off. Because food was often scarce for our ancestors, our bodies have been genetically programmed to combat the effects of fasting.

When you eat less food, your metabolism slows down to conserve energy. Then, when you go back to your usual diet, your lowered metabolism may cause you to store more energy, meaning that you will probably gain back the weight you lost and possibly even put on more weight when eating the same calories you did before the fast.

As you fast, your body will adjust by reducing your appetite, so you will initially feel less hungry. However, once you have stopped fasting your appetite hormones will return full force and you may actually feel hungrier and be more likely to binge.

Alternative day fasting

Alternative day fasting (ADF) is a bit different. It involves eating what you want one day, then a very restricted diet (fewer than 600 calories for men 500 for women) the next, and most surprisingly, it does not seem to matter that much what you eat on non-fast days.

Dr Krista Varady of the University of Illinois at Chicago carried out a 10-week trial comparing two groups of overweight patients on ADF.

Her findings concluded that ADF is a viable diet option to help obese people lose weight and to decrease their coronary artery disease risk.

"If you were sticking to your fast days, then in terms of cardiovascular disease risk, it didn't seem to matter if you were eating a high-fat or low-fat diet on your feed (non-fast) days," she said.

Dr Michael Mosley, who looked into the science, couldn't manage alternate day fasting but did a five:two ratio, five days normal eating and two days of under 600 calories.

He stuck to this diet for five weeks, during which time he lost nearly a stone and his blood markers, like IGF-1, glucose and cholesterol, improved.

He said: "If I can sustain that, it will greatly reduce my risk of contracting age-related diseases like cancer and diabetes."

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