Debating Diets: What is intermittent fasting?

Thinking about starting a new diet? While the amount of information available can be overwhelming, it’s possible to find a diet that is safe, suitable and effective for your lifestyle.

Jennifer Cleveland, registered dietitian with Baylor College of Medicine, discusses the basics of intermittent fasting.

How does intermittent fasting work?

To me, intermittent fasting is not quite a diet, but more of a meal timing pattern. There are different ways to pursue fasting: alternate-day fasting, alternate day-modified fasting and time-restricted feeding.

With alternate-day fasting, you eat every other day. On fasting days, you only consume water, coffee, and tea without added sugars or milk.

Alternate day-modified fasting is known as the 5/2 plan, where you eat normally for five days, and have a very low-calorie day two days a week. This is not a true fast, but a reduced-calorie day where you would consume about 500 calories, or the equivalent of one medium-sized meal.

The most popular form of intermittent fasting is time-restricted feeding, which allows you to eat daily, but you shorten the window of time you eat. You can opt for different time frames, such as 12 hours of fasting with a 12-hour eating window, or 18 hours of fasting with a six-hour eating window.

How did this diet become popularized?

There is a renewed interest in the circadian rhythm, and because of that, people are interested in when our bodies are designed to be awake and eating. Animal studies also reveal benefits with intermittent fasting. Many of the claims from intermittent fasting come from these studies, however these proposed benefits may or may not translate to humans and to everyday life conditions.

These claims can be overstated, which is reflected online.

Who should avoid this diet?

Women who are pregnant or lactating should avoid this plan. Individuals who are taking prescribed medication should discuss this plan with their doctor before making changes. Those with a metabolic disorder or chronic condition, such as diabetes, should first clear this plan with a physician and make a plan to monitor it with their care team.

Individuals with a history of eating disorders could see symptoms exacerbated. Athletes should consider the timing of their meals and work with their dietitian to make sure they are properly fueled for practice or competitions.

People with immune-deficiency and older adults with cognitive decline should also avoid this pattern.

What kind of physiological changes or side effects should be expected?

Although these changes may not be exclusive to intermittent fasting, individuals may see improvements in blood sugar control, blood pressure and weight loss.

Time-restricted feeding may be more feasible than other forms of fasting. The range of side effects may depend on which fasting regimen you participate in.

Adverse effects are more likely with alternate-day fasting or other more extreme fasting regimens. These may include dehydration, fatigue, negative mood, difficulty concentrating, heartburn, and constipation.

Without sufficient physical activity and protein intake, weight loss may come from muscle mass. Consider that there is limited human research on the long-term effects of fasting regimens before trying this trendy eating plan.

What else should people know before considering intermittent fasting?

If you want to try this plan, first visit with your physician to ensure you do not have a contraindication to frequent fasting. If you are pursuing time-restricted feeding, most experts agree it may be more beneficial to begin your eating window earlier in the day due to our internal clock and natural hormone pattern.

It’s still important to keep your diet quality in mind if you try this plan. Make sure you get adequate fiber from whole grains, fruits and vegetables (25 grams for women and 38 grams for men) and include good-quality protein in your diet.

Additionally, be mindful and minimize liquid calories, such as sugar-sweetened coffee drinks and sodas. Most importantly, think about which long-term healthy habits will be most sustainable for you.

Additional Resources

What is the Mediterranean diet?

See dietitian-approved recipes.

Learn about the Medical Weight Management Clinic at Baylor.

Read how Baylor promotes a culture of healthy living and wellness.

-By Homa Shalchi

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