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Intermittent fasting has extraordinary health benefits

A recent review of over 25 studies into the effects of intermittent fasting shows that this is a safe diet strategy that can result in clinically significant weight loss ( greater than 5%) and improve several markers of metabolic health, including blood pressure and insulin resistance. 

The review considered the effects of three types of intermittent fasting: 

  • Alternate day fasting, which involves a day where normal calorie intake occurs, alternating with a fast day where only a single meal of 500 calories is consumed. 
  • 5:2 diet, which is a modified version of alternate day fasting that involves five days of normal calorie intake and two fast days per week. 
  • Time-restricted eating, which confines eating to a specified number of hours per day, usually four to ten hours, with no calorie restrictions during the eating period. 

All forms of fasting reviewed in this study produced mild to moderate weight loss (1–8% from baseline) and consistent reductions in energy intake (10–30% from baseline). 

“We noted that intermittent fasting is not better than regular dieting; both produce the same amount of weight loss and similar changes in blood pressure, cholesterol and inflammation,” said Krista Varady, professor of nutrition at the UIC College of Applied Health Sciences and author of the review article.

Various studies of time-restricted eating showed participants with obesity losing an average of 3% of their body weight, while alternate day fasting resulted in weight loss of 3–8% of body weight over three to eight weeks. Studies for the 5:2 diet showed similar results, which surprised the study’s reviewers. The participants in the 5:2 diet fast much less frequently than alternate-day fasters do, but the weight loss results are similar.  

The weight loss of participants in both the alternate day and 5:2 fasting regimes is comparable to more traditional diets involving daily calorie restriction. Participants in studies of both fasting diets were able to maintain an average of 7 percent weight loss for a year. 

Professor Varady explained that the review set out to debunk some myths regarding intermittent fasting. Intermittent fasting does not negatively affect metabolism, nor does it cause an increased incidence of eating disorders, according to the studies reviewed.  

“Fasting people are worried about feeling lethargic and not being able to concentrate. Even though you are not eating, it won’t affect your energy. A lot of people experience a boost of energy on fasting days,” explained Professor Varady.

Beyond promoting weight loss, intermittent fasting may lead to other health benefits such as decreased blood pressure and insulin resistance. In some cases, cholesterol and triglyceride levels are lowered. Some studies examined for the review also demonstrated improved appetite regulation and positive changes in the gut microbiome as consequences of intermittent fasting.

The study review includes 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 undertake intermittent fasting, 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, of 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. 

“People love intermittent fasting because it’s easy. People need to find diets that they can stick to long term. It’s definitely effective for weight loss and it’s gained popularity because there are no special foods or apps necessary. You can also combine it with other diets, like Keto,” said Professor Varady. 

The research is published in the journal Annual Review of Nutrition.

By Alison Bosman, Staff Writer

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