While intermittent fasting isn’t new, it’s gained popularity again with recent research. The idea of focusing on when you eat instead of what you eat is a welcome diet approach for some people. Studies show that intermittent fasting can have many beneficial effects including lowering blood glucose and reduced insulin resistance and reduced insulin requirements. Other health benefits adding to the list are weight loss, decreased inflammation, cancer risk reduction, lower cholesterol and blood pressure, brain health, and anti-aging.
What is intermittent fasting?
There are several different ways to fast, but the three most common forms are:
- Daily time-restricted eating, or sometimes called the 16:8 plan, is fasting 16 hours and eating during an 8-hour period. For example, eating only during 12:00-8:00 p.m.
- Every other day or alternate-day fasting is eating one moderate-sized meal in the middle of the fast day and regular meals on the non-fasting day. An example of this is eating a meal around 500 calories between 12-2 p.m. on the fast day.
- Two days per week, or sometimes called the 5:2 plan is eating one moderate-sized meal on the two fast days. For example, eating one meal around 500 calories daily twice per week and eating regular meals 5 days per week.
How it works
To understand more about intermittent fasting, I went to a leading researcher in this topic, Mark Mattson, Ph.D., Johns Hopkins Medicine neuroscientist. His recent review article on intermittent fasting describes the science and practical applications.
Mattson describes the benefits of intermittent fasting are from metabolic switching. During fasting, glucose is depleted and the liver converts fatty acids to ketones to be used for energy instead of glucose. So, the switch is going from glucose to ketones. Ketones are produced 8-12 hours after the start of fasting. “Elevation of ketones is a marker of the metabolic switch, but animal studies suggest beneficial cellular responses beyond ketones” states Mattson. So even if someone is not in ketosis, there are still benefits of fasting.
I asked Mattson if there is a preferred time for fasting. “We don’t know the answer to that yet, but it’s clear that skipping breakfast can be healthy”, replied Mattson. While more research is needed, there could be a benefit of fasting from carbohydrates while including some protein and fat.
Not all studies show that intermittent fasting is superior to a low-calorie diet for weight loss. Mattson commented, “It depends on the calorie restriction and the intermittent fasting regimen. Research does support that people maintain body weight loss well with intermittent fasting and that it enhances the loss of fat.”
What are the risks?
The immediate risk is hypoglycemia for people with diabetes who take diabetes medication such as insulin and sulfonylureas. While drinking water is encouraged during fasting, dehydration could be a risk if you are used to drinking with meals. Adequate nutrient intake is also a concern if food choices are unhealthy when not fasting.
Some side effects of intermittent fasting may include intense hunger, headaches, irritability, weakness, and nausea. Mattson says it can take up to a month to adapt to a new eating pattern and feel the benefits.
Currently, Mattson doesn’t recommend intermittent fasting for people with type 1 diabetes. Other people who should not follow intermittent fasting include women who are pregnant or breastfeeding, older frail adults, young children, and people with eating disorders.
ADA does not recommend IF as a therapy for diabetes. According to ADA’s nutrition therapy Consensus Report, the studies reviewed showed that intermittent fasting may result in weight loss but didn’t improve A1C.
The bottom line
Intermittent fasting is not for everyone. Talk with your healthcare provider before trying any form of fasting, especially if you take diabetes medication. Some medications may need to be adjusted and increased glucose monitoring depending on your hypoglycemia risk. Intermittent fasting can be safe and effective for people with diabetes when medically monitored.
Mattson advises people interested in intermittent fasting to ease into it. He recommends narrowing the time window of eating. For example, for one month fast for 10 hours, then next month increase to 12 hours. This all depends on your daily routine and preferences.
Intermittent fasting isn’t a pass to eat unhealthy food when you do eat. It’s important to still follow a healthy nutrient-dense diet because you are eating less often. Remember to stay hydrated and drink more water than normal to make up for the loss of fluids from foods.