POST SUMMARY: What this means for you…
Restricting eating to a specific window of time (e.g. skipping breakfast), is a strategic way to lower insulin and improve insulin sensitivity.
A common thread among many dietary plans is compressing eating times. On the one hand, some plans narrow periods to two to three meals per day, with substantial time gaps in between (i.e. time-restricted feeding). Variation include other strategies that suggest eating normally for a few days, then avoiding food entirely for a few days (i.e. intermittent fasting). On the other hand, some diet plans encourage eating several meals throughout the day (i.e, “grazing”; 6-8 small meals per day).
Because elevated insulin is one of the most, if not the most, relevant factor in developing insulin resistance, a highly rational strategy is to follow a dietary plan that incorporates periods of time throughout the day wherein insulin is low. This philosophy immediately suggests that frequent eating is less effective than less frequent eating—indeed, three meals per day is better than six —but are fewer than three meals best of all? Maybe.
Fasting’s Effectiveness Partially Depends on How It’s Done
Time-restricted feeding and intermittent fasting strategically include periods of deliberate food avoidance. The evidence regarding its efficacy in improving insulin sensitivity is valid, though it partially depends on how it’s done. Two studies used this idea by having study subjects eat normally one day (i.e. unrestricted) and essentially fast the entire second day (i.e., alternate-day fasting), repeated seven times over a two-week period and found conflicting results—one reporting an improvement in insulin sensitivity , while the other observed no benefit . An alternative strategy, wherein the person confines eating to a specific window of time each day (e.g., eating breakfast and dinner only , or lunch and dinner only ) yielded robust improvements in insulin sensitivity.
A critical distinction must be made between thoughtful food restriction and starvation. Whereas fasting and time-restricted eating is a deliberate restriction of food daily (i.e. time-restricted eating) or for longer (i.e. intermittent fasting), each is a scheme that involves eating fully for some period of time, with deliberate restriction for only certain periods—part of a day each day or an entire day every so often. There is ideally no calorie counting with either strategy—simply avoiding food certain times and eating normally (until satiated) other times.
A Very Important, Fine Line
It may seem like splitting hairs, but there’s an important, yet fine line between eating to keep insulin low vs. starving your body. Taken to an extreme, it’s possible fasting can do more harm than good. There is no definite time past which fasting becomes harmful; so much depends on the constitution of the person fasting, how they define “fasting” (e.g. what are they drinking, how are they supplementing, etc.), and how they’re compensating for not eating essential minerals (e.g. magnesium). Importantly, early studies into prolonged fasting found a potentially lethal consequence can develop after fasting ends, termed “refeeding syndrome” . And, if not done smartly, prolonged fasting becomes actual starvation, which can paradoxically cause the body to become insulin resistant .
The Macronutrient Mix Also Affects Success
The elephant in the room with studies exploring time-restricted eating or intermittent fasting is the macronutrient content of the diet. (To my knowledge, these studies have yet to be performed.) Altering the macronutrients of the diet (e.g., carbohydrates vs. fats) may yield disparate responses not only with how well the individual can maintain the diet, but also whether it’s healthy. Whether it’s feasible and sustainable are affected predominantly by the amount of calories consumed; if a person fasts ~18 hours each day (e.g., eating from noon to 6 PM), whether this is healthy will depend on what they eat when they do eat. By consuming more of one macronutrient over another, the person may ensure they’re providing sufficient energy to the body, despite eating less total amount (i.e., volume) of food, which means increased satiety .
Making Fasting Easier
Energy (e.g., calories) from a meal conveys greater satiety than bulk—if your cells are fed, they don’t care whether there’s something in your stomach. Thus, meals that provide energy without spiking insulin (i.e. dietary fat) not only provide energy to the body, but also prevent the hunger that comes with increasing insulin , which typically makes fasting much easier.
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About Benjamin Bikman, Ph.D. – Ben earned his Ph.D. in Bioenergetics and was a postdoctoral fellow with the Duke-National University of Singapore in metabolic disorders. Currently, his professional focus as a scientist and professor (Brigham Young University) is to better understand chronic modern-day diseases, with special emphasis on the origins and consequences of obesity and diabetes. He frequently publishes his research in peer-reviewed journals and presents at international science meetings.