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Intermittent Fasting: Common Sense or Too Good to Be True?

Happy National Obesity Care Week! Did you know that only 1-2% of individuals with the condition of overweight/obesity receives medical care for this condition? Did you know that health care and pharmaceuticals for the condition is excluded from many health plans, has to be "opted into", and coverage only “kicks in” after a person develops a health condition associated with the condition? Did you know overweight/obesity is the leading cause of preventable death in the United States now? Did you know that obesity rates have risen and it is estimated that by 2030, 50% of the population in America will have obesity? The Obesity Action Coalition is one group active in addressing conditions like weight stigma, bias, discrimination, and access to equitable care. It is a cause about which I am passionate! It affects many people in many ways, and it is immensely treatable!


One question that naturally follows the alarming statistics noted above is, why has the condition of overweight/obesity become so prevalent, and why has it been so resistant to public health and other measures? Healthy People 2020 was a group of measures put forth by large institutions in 2010 to help combat obesity. Unfortunately, none of its goals were met. The prevalence of obesity has not decreased and the prevalence of super obesity has increased. Research has shown, in a nutshell, that 80% of a person’s natural weight is genetics (and epigenetics) and environment. In addition, factors like weight positive medications, orthopedic injuries, and medical conditions add to weight gain. Some people who opine that obesity is less of a disease and more of a lifestyle argue that human genetics have not changed. While this is not necessarily true, as epigenetics can change the expression of genes from one generation to another, what if we look more closely at the environmental factors? We live in a very obesogenic society, or one which promotes weight gain. One way in which that is true is the shift in the timing of caloric intake. When humans evolved, food supply was not consistent and ever present. Therefore, humans adapted to tolerate periods of intermittent fasting. In more recent history, such as when work patterns were such that people worked on farms, or in manufacturing, calorie intake was highest in the morning and during the early and mid parts of the day. The old pattern was a large breakfast, hearty lunch, and then a light supper before bed. Today, we do not work active jobs, for the most part, but in addition to that, most of the time, the timing of calorie intake is opposite: people skip breakfast or have a light breakfast, may work through lunch, then come home and consume more than half their daily calories at night at the “family dinner”. We also live in a 24 hour society, in which many people work swing shifts or graveyard shifts or just stay up really late at night. We are all aware of the fact that society currently promotes productivity over activity (sitting at your computer), and the food environment is one of ultra processed foods so that the typical American diet is 53% cabohydrate. The new research now is on the circadian effect of calorie intake. So, now only does what you eat matter, but when you eat it matters, too.


So, a dietary pattern that has received a lot of attention lately and somewhat turned into the “latest and greatest” new thing in weight loss, perhaps since “keto” is sort of old news now, is intermittent fasting (IF). What does the data show about IF and its efficacy for weight loss and health benefits? There is a lot of research on this topic. In the studies, they follow a few methods. The most common one for assessing the effect of IF on weight loss is to compare it to simple calorie restriction (CR). In calorie restriction, a person simply consumes less calories every day, such as 300 to 500 calories less per day, but all the days are the same and the timing is not specified. Most of the studies look at weight loss at 8 to 13 weeks. In a nutshell, the research shows that IF does not provide weight loss that is superior to calorie restriction, but may be better tolerated by some and may have additional cardiometabolic benefits compared to calorie restriction such as improved insulin sensitivity, for the same amount of weight loss. However, the drop out rate was still greater than 20%. The studies show that the optimal feeding period is 8 am to 2 pm. Note that this is the opposite pattern than most people follow from my anecdotal observations, in which they elect an early phase intermittent fast of skipping breakfast, which I fear, is simply rationalizing the circadian rhythm / nutrient intake discordance that theoretically contributed to the increased prevalence of obesity in the first place. The studies also show that short term weight regain is common. There are studies on using protein fortified liquid meal replacements on fasting days longer term which did not show weight regain and showed small continued weight loss (see below for how to do this).


There are additional caveats and common potential pitfalls regarding IF to consider. If you are not staying in nutritional ketosis during your feeding phases, then you may not be “fat adapted” during your fasting periods and so your muscle and brain function may be decreased. This varies from person to person. If your energy or exercise tolerance is lower when you are fasting, then there may be unaccounted for reductions in physical fitness, calories burned when not exercising (Non Exercise Activity Thermogenesis), or reduced calories burned during exercise. Perhaps related to that, some scientists opine that during fasting, lead body mass is necessarily reduced. This may be more so during more prolonged fasting, but it is important to consider, since it seems like the trend is to think that if IF is good, then the longer the fasting period, the better. Even though the studies do not show increase loss of lean body mass compared to IF with the short term studies and relatively short fasts, there may be as much as 20% loss of lean body mass with significant weight loss by caloric restriction. This can contribute to weight regain and decreases in resting metabolic rate seen with weight loss. At Rainier Medical, the body composition is followed to optimize lean body mass by tailoring a program. The goal with any weight management program is generally to reduce waist to hip ratio. So, if you notice you are losing your “glutes” but you still have evidence of the excess fat around the abdomen, this may be happening to you.


In summary, the studies show:

  • Cardio metabolic benefits to intermittent fasting that happen very quickly

  • Weight loss is the same as calorie restriction

  • Tolerability which may be slightly higher overall compared to calorie restriction

  • The drop out rate is over 20% after 12 weeks

  • Weight regain is common

  • The best feeding window is early in the day, such as 8 am to 2 pm


How can this information be implemented into a weight management strategy? My interpretation is that there are very important lessons from intermittent fasting. It can be incorporated into many different dietary plans. It likely has even more cardio metabolic benefits for people with more insulin resistance, or the potential for insulin resistance, including postmenopausal or perimenopausal women. It is important to address what to eat during the feeding time, so it is only part of a plan. It is best used by people who simply know they tolerate it better. If you do not, then be assured it is not superior for weight loss, per se, and especially will not be superior if it does not feel easier to you.


How does IF compare to the Rainier Medical plan? It is actually already incorporated, in a way, into the Rainier Medical plan. The Rainier Medical plan is a “protein sparing modified fast (PSMF).” In a caloric restriction plan, all of the calories are reduced. In this PSMF, every day is like a modified fast, in which caloric intake is reduce more than a typical caloric restriction plan. In a modified fast within the IF regime, intake is 25% of a normal day. In the Rainier Medical plan, daily intake is usually 800 kcal, but 400 of it is high quality, medically fortified, protein. Medical grade meal replacements are designed to support lean body mass, provide 100% of essential macronutrients, micronutrients and electrolytes compacted into a much reduced caloric intake in a way that is not possible with non medically formulated supplements. This is to enhance safety and support essential functions. During weight loss, we do not want lean body mass to decrease, we want fat mass to decrease. In the Rainier medical plan, a nutritional ketosis is expected after 3 days, and persists throughout the weight loss program. This induces the cardio metabolic effects and appetite suppression benefits described in the IF protocols. The difference is, the nutritional ketosis and modified fast persists throughout the weight loss phase and that is why the weight loss is more than is seen in either the IF or the CR studies, an average of 22% compared to 9-13%, on average.


I think IF may have a role for some people in weight maintenance phase. If IF reduces the chance of insulin resistance, and hyperinsulinemia precedes weight gain (see the blog on this), then perhaps a 5:2 IF plan is something highly tolerable for part of a maintenance plan. In this plan, you would follow the Rainier Medical protocol for 2 days out of every 7. The other 5 days would be “normal” calorie intake. The days may be Monday and Thursday. This may allow any excess glycogen stored up over the more liberal eating on the weekends to be utilized. Having a modified fast on Thursday would “prep” the body for the next weekend. To do this plan, you would need 5 boxes of smoothies or equivalent and 2 boxes of bars or equivalent for the month.


In summary, IF alone does not show superior weight loss to calorie restriction plans, but may show more cardio metabolic benefits and may be more tolerable for some people than restricting calories every day. IF may be a fancy name for what we were always told: breakfast is the most important meal of the day, eat breakfast like a king/queen and dinner like a pauper. Eat a light supper and don’t eat after dinner. As always, the best plan is the one that works for you. No plan works if you can’t work a plan. The best feeding window is 8 am to 2 pm. The drop out rate is high after 12 weeks and weight regain is common without a plan to follow.


For more information, read here.

For a video version of this BLOG, click here.


Take Back Your Health,


Valerie Sutherland, MD







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