In a new study from the University of Illinois Chicago, researchers found intermittent fasting can produce clinically significant weight loss as well as improve metabolic health in individuals with obesity.
They found that intermittent fasting and regular dieting both produce the same amount of weight loss and similar changes in blood pressure, cholesterol and inflammation.
According to the study, all forms of fasting reviewed produced mild to moderate weight loss, 1 percent to 8 percent from baseline weight.
Intermittent fasting regimens may also benefit health by decreasing blood pressure and insulin resistance, and in some cases, cholesterol and triglyceride levels are also lowered.
Other health benefits, such as improved appetite regulation and positive changes in the gut microbiome, have also been demonstrated.
In the study, the team looked at over 25 research studies involving three types of intermittent fasting:
- Alternate day fasting, which typically involves a feast day alternated with a fast day where 500 calories are consumed in one meal.
- 5:2 diet, a modified version of alternate-day fasting that involves five feast days and two fast days per week.
- Time-restricted eating, which confines eating to a specified number of hours per day, usually four to 10 hours, with no calorie restrictions during the eating period.
They found alternate day fasting resulted in weight loss of 3% to 8%of body weight over three to eight weeks, with results peaking at 12 weeks.
Individuals on alternate day fasting typically do not overeat or binge on feast days, which results in mild to moderate weight loss.
Studies for the 5:2 diet showed similar results to alternate day fasting. The people who participate in the 5:2 diet fast much less frequently than alternate-day fasting participants do, but the weight loss results are similar.
Weight loss with alternate day and 5:2 fasting are comparable to more traditional daily calorie-restrictive diets. And, both fasting diets showed individuals were able to maintain an average of 7% weight loss for a year.
The team also gives a summary of practical considerations for those who may want to try intermittent fasting. Among the considerations are:
- Adjustment time—Side effects such as headaches, dizziness and constipation subside after one to two weeks of fasting. Increased water intake can help alleviate headaches caused by dehydration during this time.
- Exercise—Moderate to high-intensity endurance or resistance training during food abstention can be done, and some study participants reported having more energy on fast days. However, studies recommend those following alternate day fasting eat their fasting day meal after exercise.
- Diet during fasting—There are no specific recommendations for food consumption during intermittent fasting, but eating fruits, vegetables and whole grains can help boost fiber intake and help relieve constipation that sometimes accompanies fasting.
- Alcohol and caffeine—For those using an alternate day or 5:2 fasting plan, alcohol is not recommended on fast days as the limited calories should be used on healthy foods that provide nutrition.
There are several groups who should not intermittent fast, according to the studies. Those individuals include:
- Those who are pregnant or lactating.
- Children under 12.
- Those with a history of disordered eating.
- Those with a body mass index, or BMI, less than 18.5.
- Shift workers. Studies have shown they may struggle with fasting regimens because of shifting work schedules.
- Those who need to take medication with food at regimented times.
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The study is published in the Annual Review of Nutrition. One author of the study is Krista Varady.
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