Intermittent fasting for weight loss in obese patients

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By Kellie Blake, RDN, LD, IFNCP

Obesity is a complex disease with many potential treatment avenues. In my traditional training to become a registered dietitian, I learned to encourage my overweight and obese patients to simply reduce their food intake by 500 calories per day on average to experience healthy, gradual weight loss. Fasting, despite its history of successful use in a variety of religious and medical settings, was considered unhealthy, inappropriate, and a fad diet not to be recommended. That was over 20 years ago, and we now know the calorie reduction approach to obesity is ineffective.

The research demonstrating the benefits of intermittent fasting on overall health and weight loss is growing and impossible to ignore. Obesity rates continue to rise despite the 72 billion dollars Americans spend each year on myriad products, diets, surgeries, and programs promising miraculous and lasting weight loss. While nutrition is just one piece of the complex obesity puzzle, it is nevertheless essential when it comes to healthy, sustained weight reduction.

Calorie restriction has been shown to prevent and help reverse obesity as well as numerous other health conditions. But many patients find following strict calorie-controlled meal plans difficult and long-term success and adherence are poor. Intermittent fasting, on the other hand, is a more flexible method of calorie restriction that can be practiced in many different forms, making it potentially more successful in the long run when it comes to weight loss.

Intermittent fasting improves the insulin resistance, dyslipidemia, and inflammation that are hallmarks of obesity, but also reduces deadly visceral fat, improves mitochondrial function, and increases muscle mass. As reported in the journal Obesity, all forms of fasting allow the body to flip the metabolic switch to move from using glucose to fatty acids derived from ketones for energy. Ketones are now considered to be the preferred fuel source for brain and body function, but the typical Western diet with its three meals per day and high refined-carbohydrate content make it practically impossible for ketones to be used for fuel. Instead of utilizing the ketogenic diet, which can be difficult to maintain, intermittent fasting allows the obese patient to reap the benefits of ketones, while maintaining a more normal eating pattern.

Intermittent fasting strategies can include:

• Overnight fasting: No caloric intake for a period of at least 12 hours overnight.
• Alternate day fasting: No caloric intake one day, no caloric restriction the next.
• Alternate day modified fasting: Consumption of less than 25 percent of caloric requirement alternated with days of no calorie restriction.
• Time-restricted feeding: Calorie consumption is limited to a finite period of the day such as eight to 10 hours.
• Periodic fasting: Fasting for one to two days per week and eating without caloric restriction for five to six days.
• Fasting mimicking diet: Consuming 800 to 1,100 calories per day for five days once per month.

A study published in the journal Ageing Research Reviews, several trials have shown positive results with various forms of intermittent fasting for weight loss. While weight loss was significant with both continuous calorie restriction and intermittent fasting, those practicing intermittent fasting had higher adherence rates, did not over-consume calories on non-fasting days, and reported a self-imposed calorie reduction of 23 to 32 percent on non-fasting days.

Valter Longo, PhD, reports in his research his fasting mimicking diet (FMD) research in mice and humans. In mice, the FMD increased lifespan, caused weight loss, preserved bone mineral density, reduced tumors and cut skin disorders by half, increased stem cell regeneration, and improved cognitive function. In humans, after three consecutive cycles of the FMD, abdominal fat, blood pressure, insulin growth factor one, C-reactive protein and triglycerides all decreased, muscle mass increased, and fasting blood sugar decreased in prediabetic patients.

The loss of lean body mass (LBM) is one concern when it comes to fasting and strict calorie restriction in obese patients. According to a study in the journal Obesity, one-quarter to one-third of the weight loss seen with strict calorie restriction is related to the loss of LBM. Preserving LBM is crucial for reducing insulin resistance, preserving bone density, and maintaining the basal metabolic rate to prevent the regain of lost fat mass. Intermittent fasting techniques, specifically time-restricted feeding and the FMD, seem to preserve lean body mass.

I encourage my patients to add strength training and to increase protein intake to 1.2 grams per kilogram since both have been found to preserve LBM in both strict calorie restriction and intermittent fasting programs.

Case Study

A patient of mine sought nutrition therapy related to prediabetes and metabolic syndrome. She is 62 inches tall and reported being at her highest adult weight of 200 pounds. She was eating the routine Western diet including three meals and two snacks per day but avoided dairy products. Her initial fasting blood sugar was 159mg/dL and fasting insulin level was 41.2 µIU/mL.

The initial plan included a mitochondrial food plan with emphasis on healthy fats, vegetables, and lean protein. She was instructed to eat in an eight-hour window, as well as practice 10 minutes of meditation twice daily, and to walk on the treadmill for 10 minutes after every meal.

After six weeks, the patient had lost 23 pounds and her fasting insulin level had decreased to 14µIU/mL. She reported following the meal plan, time restricted feeding, and walking, but had not yet added the meditation. She reported much improved symptoms and stated the time-restricted feeding was not as difficult as she expected. She plans to continue with her current meal plan and fasting strategy to reach her goal of 140 pounds.

An overnight fast of 12 hours is generally safe and beneficial for most patients. But stricter intermittent fasting regimens are not appropriate in some instances. I exercise caution with the elderly, pregnant women, children, and those under chronic emotional stress. In addition, being mindful of how fasting could interfere with medication use and blood sugar control are important considerations for those with diabetes. Additionally, athletes are a group where strict fasting strategies that are not well-planned could impair performance.

While intermittent fasting is not a stand-alone strategy for weight loss, it can certainly enhance a comprehensive weight reduction plan for obese patients. My patients tend to like the flexibility of intermittent fasting and report they feel less restricted and I like the ability to tailor the fasting strategy to their personal situation.

References

Anton, S.D., Moehl, K, and Donahoo, W.T., et al. (2017) Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting. Obesity (Silver Spring). Retrieved from:  https://pubmed.ncbi.nlm.nih.gov/29086496/

Longo, V. (2016). The Longevity Diet. New York, NY. Avery.

Mattson, M.P., Longo, VD, and Harvie, M. (2017) Impact of intermittent fasting on health and disease processes. Ageing Research Review Retrieved from: https://www.sciencedirect.com/science/article/pii/S1568163716302513

Willoughby, D., Hewlings, S., and Kalman, D. (2018) Body Composition Changes in Weight Loss: Strategies and Supplementation for Maintaining Lean Body Mass, a Brief Review. Nutrients. Retrieved from: https://www.mdpi.com/2072-6643/10/12/1876