Intermittent fasting could benefit patients with obesity, insulin resistance

Intermittent fasting might benefit patients with overweight, obesity, prediabetes or insulin resistance, according to a presentation at the virtual meeting of the American Society of Nutrition.

It also may be appropriate for patients with type 1 or type 2 diabetes, Kelsey Gabel, PhD, RD, a clinical assistant professor and post-doctoral research assistant in the department of kinesiology and nutrition at the University of Illinois, Chicago, said.

Evidence is “still extremely limited” on the effects of intermittent fasting for patients with diabetes, Gabel said. “Preliminary evidence does suggest that it actually may be safe in these individuals,” with the caveat that patients “should closely monitor their blood glucose,” she added.

There is even more evidence to support an intermittent fasting diet in patients with insulin resistance.

“In our year-long alternate day fasting study ... we did find that people with insulin resistance had more improvements in insulin sensitivity doing intermittent fasting versus those doing calorie restriction,” Gabel said.

Types of intermittent fasting

Intermittent fasting is typically seen as an umbrella term for three types of diets: alternate day fasting, the 5:2 diet and time-restricted eating, according to a presentation from Krista Varady, PhD, a professor of nutrition at the University of Illinois, Chicago.

Alternate day fasting is a diet in which people alternate fast and feast days; on fast days, they consume no more than 500 calories, and on feast days, they do not keep track of calories.

The 5:2 diet, which is more popular in the United Kingdom, is an alternative to alternate day fasting in which people have 2 fasting days per week.

Although clinicians are often concerned that patients who are using alternate day fasting will binge eat on the feast days, “they only eat about 10% more food, so about 200 to 300 calories more on that day,” Varady said.

“People often report feeling more in touch with fullness and hunger cues, and they're really not ravenous on the fast day, she said. “And then on the feast day, they eat normally or maybe just a little bit more.”

For time-restricted eating — the most popular form of intermittent fasting — people eat within a specific window of time each day, typically between noon and 8 p.m. so they can continue to enjoy family dinners and other social eating activities, Varady said. In studies where patients skip dinner, “we’ve had atrocious dropout rates and poor adherence,” she said.

Clinical application of intermittent fasting

Not everyone should pursue an intermittent fasting diet, according to Gabel. Some exclusionary criteria should be considered.

Intermittent fasting is not recommended in:

• children aged younger than 12 years;

• people who are pregnant or lactating;

• people who have a normal weight or BMI of less than 18.5 kg/m²;

• people who have a history of eating disorders;

• people aged older than 70 years; and

• people who need to take medications with meals.

Some feel that 12 years is a “too extreme” age to begin intermittent fasting, “as this does tend to be the peak age window for eating disorders,” Gabel said.

“However, there does seem to be evidence that points to, if the intervention is medically supervised, that those eating disorder symptoms do not increase,” she said.

At any age, adverse events should be monitored for the first 3 months — the period with the most weight loss.

“You would want to monitor [nutrient deficiencies] like vitamin D, B12, electrolytes during those first 3 months when weight loss is at its highest. Things like medications for blood pressure, lipids and glucose should be monitored. As the individual loses weight, their medications may need to be changed,” Gabel said.

She also offered advice for those considering implementing an intermittent fasting diet into their lives, like creating an eating window that is more convenient, drinking more water during the adjustment period — the first 2 weeks or so — and not holding back on protein, especially when on an alternate day diet.

References:

• Gabel K, et al. Clinical application of intermittent fasting in various population groups. Presented at: American Society of Nutrition Scientific Sessions and Annual Meeting; June 14-16, 2022 (virtual meeting).
• Varady K, et al. Human trials of alternate day fasting and time restricted eating. Presented at: American Society of Nutrition Scientific Sessions and Annual Meeting; June 14-16, 2022 (virtual meeting).