At the European Society of Endocrinology meeting in Barcelona (May 20, 2018), a study was presented that found that three months of alternating 24-hours of fasting on one day and eating unrestricted food on the next day caused rats to eat less total food and lose total body fat, but the rats developed signs of becoming diabetic. They:
• lost some of their ability to respond to insulin
• had increased levels of fat in their livers and bellies
• had damaged beta cells of the pancreas that release insulin, and
• had increased amounts of free radicals in their bloodstream that can damage the liver and pancreas, accelerate aging and even increase risk for certain cancers.
Will This Occur in Humans?
First of all, we do not know if future studies will confirm these disturbing findings that regular fasting for 24 hours may increase risk for diabetes. However, there is data to show that extended fasting periods increase free radical production that damages cells (Free Radic Res, Apr 2006;40(4):339-47) that can increase risk for diabetes (Int J Clin Pract, Mar 2006;60(3):308–314). It may be that fasting for less than 24 hours will not produce cell damage, but these studies have not been done. Studies on intermittent fasting in humans have involved times shorter than 24 hours and/or have used reduced calorie intake rather than total fasting. The safest way to use intermittent fasting may be to fast 12 or fewer hours between 6PM in the evening and 6AM the next morning.
Research Showing that Intermittent Fasting Works for Weight Loss
Obesity shortens lives by increasing risks for diabetes, heart attacks, strokes and many cancers. Intermittent fasting helps people to lose weight and slows the diseases being overweight can cause (Obesity, Feb 2018;26(2):254-268). After fasting for more than eight hours, you start to lose body fat because your body is forced to change temporarily from its main energy source of the sugar, glucose, to the fat in your body that is converted to fatty acids that pass into your bloodstream and are converted to energy to produce ketones that are also used for energy. Alternate-day partial fasting has been shown in many studies to help people lose more weight than just restricting calories every day (Obes Sci Pract, Sept 2016; 2(3): 293–302). Another study showed that fasting every third day and eating unrestricted foods on the other two days:
• made cells more insulin sensitive to lower high blood sugar and insulin levels,
• caused loss of body fat, and
• reduced inflammation by increasing vascular growth factor (VEGF) that helps form new blood vessels and activates anti-inflammatory macrophages that stimulate fat cells to burn stored fats by increasing fat cell heat production (Cell Research, October 17, 2017; 27:1309–1326).
Rationale for Fasting Overnight
A high rise in blood sugar increases risk for diabetes and can damage every cell in your body. Your body prevents a high rise in blood sugar after eating by:
• your pancreas releasing insulin to drive sugar from the bloodstream into your liver, and
• any activity that contracts your muscles.
Resting muscles draw almost no sugar from the bloodstream and what little they do draw requires insulin to do so. Contracting muscles draw sugar from the bloodstream without needing insulin. This effect of muscles not needing insulin to draw sugar from the bloodstream lasts maximally during muscle contractions and up to an hour after you stop moving. To prevent a cell-damaging high rise in blood sugar after eating, you should eat just before or within an hour after you move about and contract your muscles. The highest rises in blood sugar and the most health-damaging time to eat is before you sit and watch television or go to bed at night. Avoiding eating in the evening and overnight is an effective way to lower high blood sugar levels, high insulin levels, and overweight, and to reduce your chances for suffering the obesity-related diseases including heart attacks, strokes, and certain cancers.
Intermittent Fasting May Not Be for Everyone
Certain conditions can be worsened by fasting. You should check with your doctor if you are diabetic, have low blood pressure, take medications, are underweight, have eating disorders, or are pregnant, trying to become pregnant or breast-feeding an infant.
• Do not keep foods you want to avoid in your house where they will tempt you during the hours you plan to "fast" (sugared drinks, sugar-added foods, fried foods, foods made from flour, red meat, processed meats)
• Stock plenty of fruits, vegetables, whole grains, beans, nuts and other seeds
• Eat a healthful breakfast such as oatmeal with raisins
• Eat your main meal between noon and 6 PM. It can contain lots of the healthful foods listed above
• After 6 PM, you can drink water, but avoid foods and all drinks with calories
See Why Intermittent Fasting Works