Fasting is not a new practice. It has religious, spiritual, and political roots that date back centuries. The ancient Greeks fasted for rituals, and Hippocrates recommended medical fasting. Socrates and Plato wrote about it. And in the mid-1800s, so did E.H. Dewey in The True Science of Living. History is repeating itself with the popularity of intermittent fasting.
Intermittent fasting consists of brief periods where you eat little or no food and periods where you eat without restricting your calories.
There are three kinds of intermittent fasting:
- Alternate-day fasting: alternating days of zero calories (up to 24 hours) with days of unrestricted calories
- Modified fasting: allowing20 to 25 percent of calories on fasting days and unrestricted calories on non-fasting days (for example, the 5:2 diet)
- Time-restricted fasting: doing prolonged nighttime fasting (for example, eating from 8 a.m. to 3p.m. and not any other time of the day)
Claims and research
There are claims that fasting can help you lose weight, sleep better, live longer, decrease inflammation, and improve blood glucose levels in those with diabetes. How intermittent fasting works is not yet understood though. Research in humans found little to no significant difference in weight loss, blood pressure, or fasting glucose from intermittent fasting compared to traditional calorie restriction.
Side effects and awareness
Side effects of intermittent fasting may include, feeling hungry, cold, irritable, lethargic, or distracted, or having diarrhea. As a result, intermittent fasting may impact work performance. In comparison, these side effects are not typical in someone who makes an overall, well-balanced lifestyle change related to nutrition.
Intermittent fasting can be dangerous for people with type 1 or type 2 diabetes. Their safety can depend on their medications, and they may be at risk for hypoglycemia (low blood sugar). If you have diabetes and are thinking of trying intermittent fasting for weight loss, talk to your doctor or health care provider and certified diabetes educator.
Intermittent fasting is not recommended for those at risk for eating disorders. It could also be risky for women of child-bearing age, as it is important to maximize nutrient intake before, during, and after pregnancy while breastfeeding.
There is a lot to make up for on the days when you are not fasting since going without food means you are going without protein, vitamins, and minerals. For this reason, intermittent fasting is not recommended for children and adolescents who are growing. It also may not be advised for people using medications that need to be taken with food.
At this time, there is not enough evidence to recommend intermittent fasting. The long-term effects are unknown as well as how long it takes to see health benefits, including weight loss. Researchers are calling for more human studies, longer studies, and better follow up for these studies.
You should always to talk with your doctor or health care professional before making a lifestyle change like intermittent fasting.