Many people are seeking a diet plan that works for them, and intermittent fasting is one that recently has gained in popularity. Like most diets, it has its pros and cons, so it’s important to know what to expect if considering this option.
What is intermittent fasting?
Intermittent fasting is a regimen that cycles between brief periods of fasting with either no food or significant calorie reduction and periods of unrestricted eating. With intermittent fasting, only the time is restricted, not the type or amount of food.
There are several different versions of intermittent fasting:
- Time-restricted eating—longer or shorter fasting windows. For example, eating for 10 hours with a 14-hour fast.
- Whole-day fasting—consumption of very limited calories or 1-2 days of a complete fast.
- Alternate-day fasting—like whole-day fasting but you fast every other day.
When starting intermittent fasting, be prepared for some negative side effects. The big one is hunger. If your body is used to eating at a certain time and you change this, your body is going to let you know something is different. For instance, if you have always eaten breakfast at 8 a.m. and now your window of eating is 12-8 p.m., you may be hungrier in the morning and more irritable. However, the body has an amazing ability to adjust to its new environment and this will likely go away. In the beginning, these changes may be difficult, but the longer you do it, the easier it will become.
Is it sustainable?
For someone who is used to eating throughout the day, this would be a very difficult transition. For those who normally eat one to two meals per day and go for long stretches without eating, adherence is more likely. For those who graze and snack excessively at night, it may be helpful to have a cut-off time.
Does it work?
Time-restricted eating works but only with caloric restriction. The challenge, like with all other diets, is that it may not be sustainable to restrict yourself to only eating at certain times. Once you start adding on eating outside that window, your calorie intake starts to go up and it will be difficult to maintain any weight loss achieved.
When to avoid intermittent fasting
Some people need to avoid intermittent fasting, including:
- People with eating disorders that involve restriction, such as anorexia or bulimia nervosa
- People who take medications that require food intake or involve metabolic changes (such as diabetes)
- People who are pregnant or breastfeeding
- People in an active growth state (such as adolescents)
What does the research say?
In April 2022, a study in the New England Journal of Medicine looked at 139 patients over 12 months. They were randomly assigned to time-restricted eating (eight-hour window) or calorie restriction. Calories allowed were 1500-1800 kcal/day for men and 1200-1500 kcal/day for women (40-55% carbohydrates, 15-20% protein and 20-30% fat). This study showed similar weight loss in both groups as well as a reduction in body fat, visceral fat, blood pressure, glucose levels and lipid levels. The conclusion is time-restricted eating works if there is calorie restriction.
However, a lack of long-term studies on intermittent fasting means there are still many questions about the impact of this practice in the long run. Some questions that need to be addressed include, What are the long-term effects of intermittent fasting? How often or how long should someone fast to see a therapeutic benefit? Is it safe for everyone or for specific populations?
Until long-term studies have been done, a recommendation can’t be given at this time.
Diet quality matters more than time restriction. A diet consisting of highly processed foods, such as hot dogs, chips and soda is going to likely contribute to weight gain, whereas a diet that is high in lean protein, whole grains, fruits and vegetables may assist with weight loss.
Instead of focusing on getting fast results, make small changes and build habits you can sustain. Choose healthy food that you enjoy and can prepare consistently. Find a physical activity that you like and can incorporate most days of the week: walking, swimming, dancing and tennis are some things you may want to try.
If you need help losing weight or want to work with experts, contact us at the Weight Loss and Metabolic Center at (713) 798-6673.
By Rachel Griehs, registered dietitian at the Weight Loss and Metabolic Center at Baylor Medicine.