There has been a lot of press lately on 'intermittent fasting'. Much confusion follows on what this really entails and what some of the benefits/risks are.
Firstly, as I've been in medicine for some 15+ years, a single diet is NOT beneficial to everyone; we have to take some of this data and apply it to the patient - each of you is quite different and this entails precision medicine. Secondly, I see different terms thrown around and here are some widely accepted definitions so we are all on the same page:
Intermittent Fasting: is fasting for long periods of time, sometimes with no calories or limited calories for days.
Time-Restricted Eating: is consuming calories in a particular window of time daily, i.e., eating from 12pm-8pm or 7am-2pm.
The old adage 'a calorie is a calorie' is likely a falsehood, it likely has more to do with calorie timing. A calorie consumed at 10pm is likely metabolized quite differently than a calorie consumed in the middle of the day. Normal diurnal fluctuations in hormones are partially responsible. Additionally, larger meals are better consumed earlier in the day versus waiting until dinner to have a large number of calories. The best timing, if doing time-restricted, is eating in a window in the AM, like 7am-2pm. However, most patients end up skipping breakfast, having their largest meal at noon and stop eating in the early evening given it's a little more socially acceptable to skip breakfast than dinner.
The result of fasting can be dramatic but can be quite varied - so please utilize your provider to guide you. The most significant likely effect is reducing insulin in your body which helps prevent insulin resistance and lower blood sugars while reducing weight. Insulin is an anabolic hormone (likes to build things) - so a reduction helps drive weight loss. Also, with longer fasting periods, you enter a state of ketosis, which is when your body burns fats very efficiently.
Regardless of weight loss, it seems that some version of restriction has benefits to glucose control, metabolism and many other biomarkers we watch including A1c, fasting sugar, hsCRP inflammatory markers and even cholesterol marks.
- Dr. William Strohman, MD