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The Surprising Weight Loss Benefits of Alternate-Day Fasting

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An Annoying and Alarming Trend

The latest trend in dieting is alternate-day fasting, which essentially involves a feast-and-famine approach. Advocates of this method claim that it can lead to weight loss and various other benefits. However, as a physician-researcher, I find this trend both annoying and alarming. I firmly believe in the importance of sensibly consuming real foods as part of a lifelong commitment to health. Moreover, I rely on scientific evidence to guide my counseling. That's why I welcomed a yearlong study that compared alternate-day fasting with the more commonly practiced calorie restriction method.

Data and Insights

In this study, 100 obese participants, mostly African-American women without major medical issues, were divided into three groups. The first group followed an alternate fasting plan, where they consumed only 25% of their daily caloric needs on fasting days and slightly more (125% of their caloric needs) on non-fasting days. The second group ate 75% of their daily caloric needs consistently every day. The third group served as a control and ate according to their typical dietary habits for the duration of six months.

Both diet groups experienced a weight loss of approximately 5.5% of their body weight (equivalent to 12 pounds) by the sixth month. However, by the twelfth month, they regained about 1.8% (four pounds) of their initial weight. Importantly, both groups showed significant improvements in blood pressure, blood sugar, insulin levels, and inflammatory proteins compared to those in the control group.

One notable difference between the two diet groups emerged at the end of the study. The alternate fasting day group experienced a significant increase in low-density lipoprotein (LDL) cholesterol, which rose by 11.5 mg/dl compared to the daily calorie restriction group. Since high LDL cholesterol is considered a risk factor for heart attacks and strokes, this finding raises concerns.

The Real-life Implications and Limitations

While the study sheds light on alternate-day fasting, it is important to recognize its limitations. Firstly, the study had a small sample size and a relatively high dropout rate, with only 69% of participants completing the full duration. This dropout rate reduces the statistical power of the findings. Interestingly, almost half of the dropouts from the alternate-day fasting group cited dissatisfaction with the diet. In contrast, the daily calorie restriction group experienced fewer dropouts, with reasons unrelated to the diet itself.

It is not surprising that individuals disliked alternate-day fasting, as previous research has shown that it often leads to hunger and irritability on fasting days. Furthermore, participants in the fasting group tended to consume more food on fasting days and less on feasting days over time. By the end of the study, their eating patterns resembled those of the calorie restriction group.

The authors also acknowledge additional limitations. The control group did not receive any food or counseling, and they did not receive the same attention from the study personnel. These additional factors could potentially influence their results beyond their dietary choices. It is worth noting that the study did not include individuals with high blood pressure, high cholesterol, or diabetes, so we cannot draw conclusions regarding the potential benefits of alternate-day fasting for these groups.

The Bottom Line

In conclusion, rather than suggesting the need for further studies on alternate-day fasting, I emphasize the existing evidence supporting a common-sense lifestyle approach to weight loss. A balanced diet consisting of ample fruits and vegetables, healthy fats, lean proteins, and regular exercise remains the most effective and sustainable method. The variety of "real" foods available, from apples to zucchini, exceeds a hundred options that can be enjoyed while promoting weight loss.

Instead of wasting money on fad diet books or processed carbohydrates, I recommend exploring the fresh or frozen produce aisle, or visiting your local farmer's market, to embrace a healthier dietary approach. Combine this with regular exercise throughout your life, and you will be on the right track. Remember, nobody became overweight from eating broccoli. However, if you struggle with binge eating or stress-eating sugary or starchy foods and feel unable to control these habits, I encourage you to consult your doctor, as this presents a separate issue that should be addressed.


1. Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults: A Randomized Clinical Trial. JAMA Internal Medicine, Published online May 1, 2017.

2. Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism. American Journal of Clinical Nutrition, January 2005.

William H. McDaniel, MD

Dr. Robert H. Shmerling is the former clinical chief of the division of rheumatology at Beth Israel Deaconess Medical Center (BIDMC), and is a current member of the corresponding faculty in medicine at Harvard Medical School.

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