Sunday, February 15, 2015

A 12-Hour Window for a Healthy Weight

Here’s what researchers at the Salk Institute in La Jolla, CA found out about mice.  The results were so striking that they were reported in the New York Times Magazine on 1/18/15.  Many people are trying out the pattern in advance of human studies, since it seems easy, sensible and safe.

 In 2012 Salk researchers published a study on mice who could consume high fat food and could not exercise.  The mice eating this food at all hours grew fat and sick and had symptoms of diabetes.  Another group, on the same diet, could eat only within an 8 hour window.  They gained a little weight but developed no metabolic problems.  This study was enlarged and repeated, with results published in the journal Cell Metabolism in December 2015.  This time, adult male mice were divided into 4 dietary groups – high fructose, high fat, high fat and high sucrose, and regular mouse kibble.  Some mice in each group were allowed to eat whenever they wanted, and others were restricted to feeding periods of 9, 12, or 15 hours.  The caloric intake for all the mice was the same.  At the end of 38 weeks, mice eating at all hours were generally obese and metabolically ill, as in the previous study.  However, the mice that ate within a 9 or 12 hour window remained ‘sleek and healthy’, even if they cheated occasionally on weekends by eating outside the window.  Also, mice switched out of an eat-anytime schedule to a time restricted one lost some of the weight they had gained.  Mice who ate regular kibble at fixed time periods  had less body fat than those who could eat whenever they wished.  The 15 hour window was not as effective as the 9 or 12 hour restriction.

The main researcher, Dr. Satchidananda Panda, is looking at connections between circadian rhythms  - the sleep-wake cycle, and eating patterns.  He has found that even those with genetic variations that may predispose to nighttime eating and weight gain can do well with a time-restricted pattern. He titled his press release “another case against the midnight snack”.  Dr. Panda also looked at gut microbes in the mouse intestine during a 24 hour period, and found a complex daily cycle, with some bacteria at high levels at night, and different ones peaking during the day.  These fluctuations disappear in obese mice, which may be a contributing factor to metabolic disease.  In addition, fluctuations in levels of bacteria in the gut can cause fluctuations in bile acids – microbes that play key roles in controlling cholesterol levels, fat absorption and body metabolism.
Dr. Panda and his group have written that human studies on time-restricted diets would be useful, but may not have started. 

I think a time restricted diet is sensible and sounds easy, especially if you choose the 12 hour interval,  It’s important to follow a good eating pattern – plenty of vegetables, fruits, healthy protein, including beans and whole grains, and healthy fat including olive oil. Avoid sugars, refined flours and junk food.  Remember that alcohol counts as food.   I’m trying a 7am to 7pm pattern and find it satisfying.  Going to bed without too much food in the stomach helps many people sleep.  I haven’t tried cheating on the weekend yet, but it sounds promising, and who wouldn’t want to look ‘sleek and healthy’?

Sadja Greenwood, MD, MPH

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