A study from Brazil found that having rats fast for 24 hours on alternate days increased their belly fat and interfered with the ability of insulin to control blood sugar levels (reported at the European Society of Endocrinology annual meeting, May 21, 2018 in Barcelona, Spain). This could have special meaning for the 50 percent of North American adults who have diabetes or pre-diabetes, because the most common cause of diabetes today may well be excess fat in the liver. To get excess fat out of the liver, almost all diabetics and pre-diabetics (also called metabolic syndrome) are advised to lose weight. One of the most effective ways to lose weight is “intermittent fasting”, but this study suggests that doctors need to be careful about the type of “fasting” they recommend to their patients.
Types of Intermittent Fasting
Several different patterns of intermittent fasting have become popular, including:
• Time-restricted fasting (every day), such as not eating after 6PM until the next morning.
• Alternate day fasting: a 24-hour “fast” followed by a 24-hour non-fasting period.
• Weekly variations such as “fasting” two days a week and five days with the person’s normal meals. The fasting does not have to be on consecutive days.
• Monthly variations such as “fasting” five days a month.
Except for the time-restricted fasting (in which you eat nothing at all for 12-16 specified hours each day), these programs typically do not recommend complete avoidance of food. For example, on “fast days” the person might eat about 600 calories in meals or snacks, compared to their normal consumption of 2000-3000 calories or more per day.
However, some people might adopt a literal definition of “fasting” and try to avoid all foods for periods of 24 hours or more. If the findings of this new rat study are found to apply to humans, total fasting for extended periods could do more harm than good. People who regularly avoid food for more than 12-16 hours may be at increased risk for becoming diabetic if they regain their lost weight, and people who are already diabetic may find that regaining the lost weight makes their diabetes worse than it was beforehand because of increased fat deposition in the liver.
Findings from the Study on Rats
Thirty-day-old female rats were fasted for 24 hours every other day and allowed to eat all they wanted on the alternate days. At the end of three months:
• The amount of fat in their bellies increased, and the amount of fat in their livers increased also.
• They developed insulin resistance. (Insulin resistance means that insulin does not lower blood sugar adequately by its usual method of driving sugar from the bloodstream into the liver).
• They lost weight because they ate less total food during the three months of the test.
• Their stomachs increased markedly in size, apparently because they ate more than usual on their non-fast days.
• They had more belly fat and less muscle than when they started the study. (Any weight loss will include some loss of muscle).
• They had higher blood insulin levels both fasting and after a glucose feeding, which would probably mean that their blood sugar levels were rising higher after they ate.
• Their pancreases were smaller than normal, but produced more insulin and free radical reactive oxygen species. Free radicals are chemicals that damage cells.
Why a Fatty Liver is Dangerous
Blood sugar almost always rises after you eat. If your blood sugar rises too high, sugar can stick to the outside membranes of cells and destroy these cells. To keep blood sugar levels from rising too high, your pancreas releases insulin that lowers blood sugar by driving sugar from the bloodstream into the liver. However, if your liver is full of fat, the liver cannot accept the sugar and blood sugar levels rise even higher, which can damage every cell in your body and make you diabetic. Most people who have a big belly and small buttocks are already diabetic as they tend to store fat primarily in their belly and liver. People who have both a big belly and big buttocks may or may not be diabetic. Your doctor can check for excess fat in the liver with a sonogram.
Nighttime is the Worst Time to Eat
The most fattening time to eat is in the evening or just before you go to bed, because you don’t contract your muscles very much when you sit on the couch or lie down. After you eat, your blood sugar rises and there are only two places that store significant amounts of sugar: your muscles and your liver. Resting muscles remove almost no sugar from your bloodstream and what little they can remove requires insulin to do so. On the other hand, contracting muscles remove tremendous amounts of sugar from your bloodstream and don’t even need insulin. When you eat and do not move much afterwards, blood sugar levels rise very high. To keep blood sugar levels from rising too high, your pancreas releases insulin which drives sugar into muscles and liver, and then converts what extra sugar remains to a type of fat called triglycerides. The extra triglycerides are stored as fat in your liver, other organs and fat cells.
My Recommendations
Many papers show that intermittent fasting can help people lose weight and slow the diseases caused by being overweight (Obesity, Feb 2018;26(2):254-268). In one recent study, 23 morbidly obese adults, average age 45, were allowed eat anything they wanted for eight hours between 10 AM and 6 PM, but they were allowed to drink only water and eat no food during the remaining 16 hours (Nutrition and Healthy Aging, June 2018, 4(4):345). After 12 weeks, they had lost an average of three percent of their weight and had a 7 mm drop in systolic blood pressure. Compared to people on other types of intermittent fasting diets, they had the same measures of insulin resistance and cholesterol.
So far, research has not proven any one method of intermittent fasting to be superior to the other methods, but based on these recent studies, I think that the safest and most effective way to lose weight and keep it off may be to avoid eating any food from 6:00 PM to the next morning. Diana and I have been using variations of this method for several years and find it very easy to do. See:
Why We Use Intermittent Fasting
Weight Loss with Intermittent Fasting
Overnight Fasting
Why Intermittent Fasting Works
Caution: Intermittent fasting is not for everyone. Certain conditions can be complicated or worsened by fasting. Please 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.
Checked 7/5/23
