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Intermittent Fasting for Weight Loss: 4 Reasons Why It Works Well

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David is a biomedical scientific officer and writer who uses intermittent fasting as part of his own health and fitness regimen.

Intermittent fasting is great for weight loss

Intermittent fasting is great for weight loss

Fasting for Weight Loss

Many people struggle with their weight for their entire lives. They try diet after diet, and although they may lose some weight for a while, it usually just goes right back on again. But successful weight loss really just comes down to one thing: consuming fewer calories than you expend (i.e. eating at a calorie deficit). And the easiest way to do that is to use intermittent fasting.

Intermittent fasting works so well because it’s not a 'diet' as such. It's more of a lifestyle. You simply choose to go without food for a set period of time on a regular basis. This could be about 24 hours once or twice per week, or just 16 hours each day—which is basically just skipping breakfast.

During the fasting period, all you will consume is water, or perhaps a little black, unsweetened tea or coffee. But the real beauty of this is it's so flexible. You can do it as and when you want, and fit it into your lifestyle in a way that best suits you. On your non-fasting days, you can eat pretty much what you want, although you will obviously have more success if you stick mostly to healthy food choices.

There are a number of reasons why fasting for weight loss works so well. But here are the top four of them:

1. You Consume Fewer Total Calories per Week

To lose weight you obviously need to consume fewer calories than you expend. But it's much better to think of your calorie consumption in weekly terms rather than in daily terms. That way if you do overeat on any one day it doesn't really matter, as you can easily make up for it the next day. And if you practice intermittent fasting you'll be eating fewer meals each week, so you'll be taking in fewer total calories—even if you eat just as you normally would the rest of the time.

2. You Produce More Fat-Burning Hormones and Enzymes

Most of our bodies' metabolic activities, including fat burning, are controlled by hormones. And hormones, in turn, need enzymes in order to work properly.

Fasting causes you to produce much higher levels of growth hormone, which is our main fat-burning hormone. It also causes an increased production of two of the most important fat-burning enzymes. These are hormone-sensitive lipase (HSL), which aids in the release of fat from fat cells, and lipoprotein lipase (LPL), which aids in the uptake of fat by muscle cells, where it is used for energy.

You also produce much less insulin when fasting, which means you’ll be able to burn off body fat much more effectively. In fact, it’s almost impossible to burn fat when insulin levels are high.

3. You Burn Fat Rather Than Sugar

When you eat your body normally burns the carbohydrate (sugar) from your meal first, and then it starts to burn fat. But any calories that are not used up within a few hours are just stored in your body as fat.

In the fasting state this changes however, and your metabolism shifts from burning sugar to burning most body fat for energy. And this effect increases over time; so toward the end of a fast (particularly one lasting 24 hours), you will be burning far more fat than you ever would during a normal day of eating.

4. It's Easy to Stick to

This is perhaps the most important point. With intermittent fasting you only need to deprive yourself for short periods of time, and the rest of the time you can eat as normal. So that means you can still eat all your favorite foods, and you won't have to concern yourself with trying to follow any particular "diet". And although at first, you might find going without food for a while a bit of a challenge, it will get easier, and you will soon come to enjoy it.

All this means you’ll find it very easy to stick to, so you’ll be able to lose weight easily and then keep it off—for life!

It's a myth that going without food for short periods of time will cause your metabolism to slow down, or put you into 'starvation mode'. It takes a lot more than 24 hours for that to happen. And in fact during a short fast your metabolism may actually increase a little, and you'll burn fat whilst preserving muscle tissue. This is something which cannot be said of your typical calorie restriction diet.

Intermittent fasting is a part of many popular and effective dietary regimens, such as Martin Berkhan's Leangains and Jason Ferruggia's Renegade Diet, which both employ 16-hour fasting periods, done on a daily basis. Brad Pilon on the other hand recommends 24-hour fasts, done every 3 to 7 days, and his book Eat Stop Eat gives a huge amount of information on the benefits and practice of periodic fasting.

If you choose to use intermittent fasting for weight loss you'll find it's the simplest way to achieve your ideal weight there is. But more importantly, it's the most effective way to maintain it. And apart from that, it has a number of exceptional health benefits too. So why not give it a go?


Heilbronn, L. K., Smith, S. R., Martin, C. K., Anton, S. D., & Ravussin, E. (2005). Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism. The American journal of clinical nutrition, 81(1), 69–73.

Ho, K. Y., Veldhuis, J. D., Johnson, M. L., Furlanetto, R., Evans, W. S., Alberti, K. G., & Thorner, M. O. (1988). Fasting enhances growth hormone secretion and amplifies the complex rhythms of growth hormone secretion in man. The Journal of clinical investigation, 81(4), 968–975.

This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

Questions & Answers

Question: I've been religiously doing the 16 hr fast 4 days a week for 6 weeks. I've lost about 2 lbs! I m 67, 5’5 and 135 lbs. I walk a mile daily and do yoga. I m getting so discouraged. What am I doing wrong?

Answer: Probably nothing really. What you are doing is great for general health purposes, but if you want to lose more weight you need a slightly more rigid approach. Do the 16 hour fast at least 6 days per week, and watch your calorie intake during your eating window. You need to be in a deficit, which is best accomplished by sticking mostly to natural, whole foods, with plenty of vegetables, and not too much fat. On your off day, you can have some "cheat foods", but don't go too far, as you could easily undo the entire weeks efforts if you are not careful.

© 2012 David