The Truth about Intermittent Fasting

from Feb 16th Edition 2023

Wellness The Gift of Failure

Bracha Abramson, RD

Can feast or famine be the key to maintaining weight loss and promoting good health? The diet fad known as Intermittent Fasting (IF) is an eating pattern where one alternates between periods of eating and periods of fasting.

The IF began to trend when British journalists Michael Mosley and Mimi Spencer published their book “The Fast Diet” in 2013. In their publication and TV documentary “Eat Fast, Live Longer,” they advocate 5:2 Intermittent Fasting. Meaning, for two days per week one limits themself to a very low level of calories, and for the remaining five days, they eat as they normally would. The logic is that after hours without food consumption, insulin levels in the blood will decrease. This will allow fat cells to release their stored fat, which can then be used for energy. The longer insulin levels are decreased, the more fat is burned which results in weight loss. Since then, many methods of IF have evolved.

The most commonly studied approaches of IF are alternate-day fasting (ADF), modified IF, time-restricted feeding (TRF), and religious fasting.

1. ADF involves a repeated cycle of one “fast” day (when only calorie-free beverages are allowed) alternating with one regular eating day.

2. Modified IF is limiting calorie intake on two non-consecutive days and the remaining five days of the week eating as one normally would.

3. TRF is typically the approach that most people associate with IF. One can eat within a limited eight-hour window and fast for the remaining sixteen hours of the day. One might eat between 9 AM and 5 PM or 12 PM and 8 PM, allowing most of their “fast” to take place overnight. One can adjust these times to their preferred eating times. This is likely the most realistic method of IF as many people tend to already eat daily in a similar pattern.

4. Religious fasting: The Jewish world is very familiar with the various established Fast Days that we have throughout the year. Some fasts involve no eating or drinking from dawn until after nightfall, while Yom Kippur and Tisha B’Av last over 24 hours. Could it be that these Fast Days can play a role in our health?

Most research conducted on IF involves animal studies, however, some findings with human subjects in the last ten years have piqued the clinical world’s interest.

Current research has shown that ADF and Modified IF are not more effective than your average calorie-restricted diet to promote weight loss. These dieters also had the lowest compliance rate and the highest drop-out rate as people reported difficulty adhering to their diets. A study conducted at the University of Alabama found that syncing one’s eating time with the body’s circadian rhythm, a version of TRF, can promote the healthiest weight loss outcomes when combined with a healthy diet and lifestyle. Eat during optimal metabolism function in the early hours of the day and reduce nighttime eating. During fast times, caloric intake is decreased, producing a negative energy balance and promoting weight loss. Maintaining this weight loss will be more difficult due to hunger and compliance with such a strict eating routine. Therefore, the most significant underlying benefit of TRF is something that we have known for years: restricting nighttime eating and fasting for longer overnight intervals not only sustains weight loss, but also improves metabolism and lowers blood sugar levels. Other reported benefits are improved cognitive function and positive effects on diseases such as cancer and diabetes.

IF, like any restrictive diet, can cause a variety of symptoms such as hunger, fatigue, headache, low energy, and irritability. Alternating fast days can also cause GI issues such as gas, bloating, and constipation. Variations of fasting can cause one’s body to go into starvation mode, wherein one would actually gain more weight when returning to a normal eating routine. There is also a concern that IF can put dieters at risk of not meeting their nutritional needs which can, in turn, result in nutrient deficiencies. This is why there is no one diet that fits all and one must consult with their own RD to assess possible contraindications and find the best approach for their body and lifestyle.

The bottom line is IF may just be another trendy diet where all it is doing is effectively causing dieters to “eat less.” By shortening one’s eating window, they are naturally decreasing their caloric intake resulting in weight loss. This decrease in weight will likely not be able to be maintained long-term if one finds their diet too difficult. However, one noteworthy fact that continues to be proven is that simply avoiding nighttime eating is extremely beneficial for overall health.