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IF as a weight loss approach has been around in various forms for ages, but was highly popularized in 2012 by BBC broadcast journalist Dr. Michael Mosley’s TV documentary Eat Fast, Live Longer and book The Fast Diet, followed by journalist Kate Harrison’s book The 5:2 Diet based on her own experience, and subsequently by Dr. Jason Fung’s 2016 bestseller The Obesity Code. IF generated a steady positive buzz as anecdotes of its effectiveness proliferated.

The information you share, including that which might otherwise be Protected Health Information, to this site is by design open to the public and is not a private, secure service. You should think carefully before disclosing any personal information in any public forum. What you have written may be seen, disclosed to, or collected by third parties and may be used by others in ways we are unable to control or predict, including to contact you or otherwise be used for unauthorized or unlawful purposes. As with any public forum on any site, this information may also appear in third-party search engines like Google, MSN, Yahoo, etc. Your use of this site is governed by Harvard University and its affiliates Terms of Use located at www.health.harvard.edu/privacy-policy and may be amended from time to time.
When your body burns its stores of fat, it can be hard on your kidneys. And starting a ketogenic diet -- or going back to a normal diet afterward -- can be tricky if you’re obese because of other health issues you’re likely to have, like diabetes, a heart condition, or high blood pressure. If you have any of these conditions, make diet changes slowly and only with the guidance of your doctor.
IF as a weight loss approach has been around in various forms for ages, but was highly popularized in 2012 by BBC broadcast journalist Dr. Michael Mosley’s TV documentary Eat Fast, Live Longer and book The Fast Diet, followed by journalist Kate Harrison’s book The 5:2 Diet based on her own experience, and subsequently by Dr. Jason Fung’s 2016 bestseller The Obesity Code. IF generated a steady positive buzz as anecdotes of its effectiveness proliferated.
H. Guldbrand, B. Dizdar, B. Bunjaku, T. Lindström, M. Bachrach-Lindström, M. Fredrikson, C. J. Östgren, F. H. Nystrom, “In Type 2 Diabetes, Randomisation to Advice to Follow a Low-carbohydrate Diet Transiently Improves Glycaemic Control Compared with Advice to Follow a Low-fat Diet Producing a Similar Weight Loss,” Diabetologia (2012) 55: 2118. http://link.springer.com/article/10.1007/s00125-012-2567-4.
The scale is not necessarily your friend. You may want to lose fat – but the scale measures muscles, bone and internal organs as well. Gaining muscle is a good thing. Thus weight or BMI are imperfect ways to measure your progress. This is especially true if you’re just coming off a long period of semi-starvation (calorie counting), as your body may want to restore lost muscles etc. Starting weight training and gaining muscle can also hide your fat loss.

The information you share, including that which might otherwise be Protected Health Information, to this site is by design open to the public and is not a private, secure service. You should think carefully before disclosing any personal information in any public forum. What you have written may be seen, disclosed to, or collected by third parties and may be used by others in ways we are unable to control or predict, including to contact you or otherwise be used for unauthorized or unlawful purposes. As with any public forum on any site, this information may also appear in third-party search engines like Google, MSN, Yahoo, etc. Your use of this site is governed by Harvard University and its affiliates Terms of Use located at www.health.harvard.edu/privacy-policy and may be amended from time to time.
When you eat less than 50 grams of carbs a day, your body eventually runs out of fuel (blood sugar) it can use quickly. This typically takes 3 to 4 days. Then you’ll start to break down protein and fat for energy, which can make you lose weight. This is called ketosis. It's important to note that the ketogenic diet is a short term diet that's focussed on weight loss rather than the pursuit of health benefits. 
Gary D. Foster, Ph.D., Holly R. Wyatt, M.D., James O. Hill, Ph.D., Brian G. McGuckin, Ed.M., Carrie Brill, B.S., B. Selma Mohammed, M.D., Ph.D., Philippe O. Szapary, M.D., Daniel J. Rader, M.D., Joel S. Edman, D.Sc., and Samuel Klein, M.D., “A Randomized Trial of a Low-Carbohydrate Diet for Obesity — NEJM,” N Engl J Med 2003; 348:2082- 2090. http://www.nejm.org/doi/full/10.1056/NEJMoa022207.
Young males sometimes lose weight faster than this, perhaps twice as fast. Post-menopausal women may lose at a slower pace. People on a very strict low-carb diet may lose weight quicker, as well as those who exercise a lot (a bonus). And if you have an enormous amount of excess weight to lose you could start out much faster — although initially, some of the weight you lose will be due to water loss.
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