I’m sure that most, if not all, of you have heard that when dieting to lose weight, it is vital to eat often as it will “stoke the metabolic fire.” This belief goes hand in hand with the idea that if your body is not given food frequently enough that you will go into “starvation mode” where your body’s metabolism decreases and you begin to burn muscle as fuel. When I was younger, I completely bought into this because the argument made sense to me. If I didn’t eat often then my body would begin to break down muscle mass due to muscle being metabolically costly. My body would want to get rid of some of the muscle so that it would take less overall calories to sustain life. This is surely some kind of survival mechanism… Or so I thought.
As I mentioned in my first post on this blog, I become obsessed/enthralled with different topics easily and often. During my first year of physical therapy school I became completely captivated by nutrition and weight loss. I spent countless hours reading research and diet books to try to find the optimal diet and the truth about nutrition. Part of this was for my own benefit to assist in my weight loss journey, but most of the reason was because I was sick of always hearing conflicting information about how to eat to lose weight and for optimal health.
I learned a lot about nutrition during about a year time span and made huge progress with my own physique implementing my new found knowledge and a good strength training program (pics at the end of this post :D). What I found shocked me at the time, but in the years since with my new knowledge base I mistakenly began to assume, since the research is plentiful, that everyone in healthcare probably had a general understanding of the current evidence on nutrition. Since then, what I’ve heard from friends, acquaintances, physicians, and in the clinic regarding diet and nutrition has baffled me. I would expect many lay people and patients to be uneducated regarding current research, but far too often I’ve heard extremely outdated myths being perpetuated by my fellow clinicians. What I find even more intriguing is that these beliefs are so strongly held, yet unsubstantiated, that instead of listening to my explanation of the evidence, people will blindly claim that the information is incorrect. These ideas seem to be ingrained in many people, but their only reasoning is that “I once read it somewhere” or “I’ve always heard…” Although I am a DPT and had limited education in school on diet and nutrition, I believe that it is vital for all healthcare workers to have a basic understanding of diet and nutrition (not based on word of mouth) due to the extremely high incidence of obesity and chronic disease in our society today. Not to mention, patients often seek general diet and nutrition advice when being treated in the outpatient physical therapy setting.
I’m here to tell you that eating often to boost your metabolism is a fallacy. The evidence is overwhelming that eating more frequent meals has minimal or possibly no effect on metabolism, overall body mass, or overall fat mass. Instead, it is overall calorie balance throughout the day that has the biggest effect on weight gain/loss. So where did this “stoking the metabolic fire” argument originate then if it isn’t true? Well it is actually quite simple. When a person ingests food, there is a temporary increase in metabolic rate. This boost in metabolic rate is caused by the thermic effect of food. What this means is that your body has to expend energy to break down the macronutrients (carbohydrates, fats, protein) that you ingest. Each macronutrient has a different thermic effect. This was incorrectly extrapolated to assume that by eating more often, your metabolism will remain elevated. The important thing to understand is that this increase is directly proportional to the amount of calories and the macronutrient composition of the meal eaten. The reason that this is so important is because as long as overall caloric load and macronutrient composition is equated, you could eat all your food in six meals or in one meal and the metabolic effect will be about the same.
A great meta-analysis regarding the effect of meal frequency on body composition was performed by Brad Schoenfeld, Alan Aragon, and James Krieger. Their results show a small improvement in fat loss from more frequent meals, but these findings could be completely negated with the removal of one of the fifteen studies included. Here is a direct excerpt from their conclusion, “The positive relationship between the number of meals consumed and improvements in body composition were largely attributed to the results of a single study, calling into question the veracity of results. Moreover, the small difference in magnitude of effect between frequencies suggests that any potential benefits, if they exist at all, have limited practical significance. Given that adherence is of primary concern with respect to nutritional prescription, the number of daily meals consumed should come down to personal choice if one’s goal is to improve body composition.”
So based on this study there may be a benefit to increased meal frequency, but the effect is likely very small and should not replace an individual’s personal preference on meal frequency.
Now let’s look at another recent study that reviewed the current evidence on intermittent fasting. Valter Longo and Mark Mattson found that the current literature supports intermittent fasting for not only reduction of body fat, blood pressure, and inflammation, but also for reducing the likelihood of developing diabetes and cancer! Add to that the fact that fasting has been shown to extend life expectancy and possibly have a neuroprotective effect on the elderly, and it’s hard to discount it as an effective nutritional strategy. Here is a quote from the conclusion of this study, “Based on the existing evidence from animal and human studies described, we conclude that there is great potential for lifestyles that incorporate periodic fasting during adult life to promote optimal health and reduce the risk of many chronic diseases, particularly for those who are overweight and sedentary. Animal studies have documented robust and replicable effects of fasting on health indicators including greater insulin sensitivity, and reduced levels of blood pressure, body fat, IGF-I, insulin, glucose, atherogenic lipids and inflammation. Fasting regimens can ameliorate disease processes and improve functional outcome in animal models of disorders that include myocardial infarction, diabetes, stroke, AD [Alzheimer’s Disease] and PD [Parkinson’s Disease]… Several variations of potential ‘fasting prescriptions’ that have been adopted for overweight subjects revolve around the common theme of abstaining from food and caloric beverages for at least 12 – 24 hours on one or more days each week or month, depending on the length, combined with regular exercise.”
In a study performed by Bhutani, Klempel, Berger, and Varady results indicated that having participants perform alternate day fasts (24 hour fast every other day) resulted in a reduction of body fat mass as well a several other coronary heart disease risk factors. Another surprising finding in this study is that although fat mass was significantly reduced, lean body mass stayed virtually identical throughout the protocol. Keep in mind that this study involved an entire 24 hours with no food multiple times per week. This certainly seems to destroy the previous theory regarding “starvation mode” with extended periods of not eating. In actuality, these people maintained their lean mass while breaking down adipose tissue for energy while not eating for an entire day.
In this study not only was there not a reduction in metabolism during a period of short term starving (fasting), but there was actually an increase in metabolic rate! The results from these studies may seem shocking for many that have heard and read that they need to eat constant small meals to lose weight, but if you look at things from an evolutionary perspective, it shouldn’t be surprising. It is certainly likely that our ancestors had to sustain periods of fasting, but not by choice. Food was often scarce and they may have had to go for days at a time with little or no food. If the “starvation mode” idea was correct then they would have lost significant amounts of muscle mass during those periods of time. What actually happens with periods of fasting is that sympathetic nervous system hormones are released and excess adipose tissue is broken down for fuel. Of course this is only up to a certain amount of time. At some point (probably in the 48-72 hour range) muscle mass will undoubtedly begin to be broken down at a faster rate, but there is no risk of this when going short periods without food.
Based on the studies above, abstaining from food for between 12-24 hours on one or more days each week or month had a significant impact on multiple conditions, including reducing body fat and improving insulin sensitivity. Reduced insulin sensitivity is what will eventually lead to type 2 diabetes which is now rampant in our population, therefore improving insulin sensitivity will help reduce the risk of developing this disorder. Now you might be realizing that these results fly directly in the face of the outdated theories regarding “starvation mode” happening when eating less often and increased metabolism happening by eating more often. This is important to understand. Recommending that everyone eat more often and to always eat breakfast may not only be incorrect, but could also be detrimental to the individual’s overall health.
Although the meta-analysis on meal frequency and the other studies on fasting are slightly in conflict with each other regarding the best diet for body composition, I believe that it is clear that a potential small improvement in body composition and reduction in fat mass from increased meal frequency is not worth foregoing the many benefits of abstaining from food for a period of time (i.e. fasting), which will undoubtedly mean less overall meals per day. As the authors in the fasting study mention, this is not something that would need to be done every day but “one or more times per week.” Let’s say an individual does undergo a 16 hour fast once or twice per week, what should they do on the other days in regard to number of meals and meal frequency? This should be left to their own discretion based on the number of meals per day that allows them to eat the most quality, nutrient dense food possible while avoiding “snacking” on processed sugary foods. In my opinion this is a big problem with promoting increased meal frequency. Some people may incorrectly assume that eating a sugary, high calorie snack is actually better for them than not eating at all because of their beliefs about starvation mode and a reduction in metabolic rate.
You may be wondering why I chose to discuss studies that involve fasting. The reason for this is not that I believe it is the best for everyone, but instead because it shows that reducing meal frequency and skipping meals does not result in the effects that are mistakenly repeated by many. If foregoing food for 24 hours or more does not result in a reduction of metabolic rate or a reduction of muscle mass, then it is clear that skipping breakfast or another meal during the day will have no detrimental consequences. Repeating the myth “breakfast is the most important meal of the day” may result in a busy individual choosing pop-tarts for a quick breakfast. Based on the research that person would be much better off skipping breakfast and replacing those calories with more nutrient dense options later in the day.
After experimenting with my diet and my body for over a year, I figured out what works best for me. I began intermittent fasting about four years ago and have been practicing different lengths of fasts since then. As I stated above, this is not the answer for everyone. It is important to consider past medical history, especially diabetes, before attempting any sort of fasting. Based on the research, the best recommendation that can be made to an individual is to eat the number of meals that allows them to make the most nutrient dense food choices and that fits their lifestyle. For some this could mean two meals a day and for others it could mean six. Both of these frequencies are perfectly acceptable in the right context.
The physique below (summer 2014) was achieved with fasting periods of between 16-22 hours per day. My “breakfast” was usually around 4-5 PM each day and occasionally I would only eat one large meal per day. While dieting down to this condition, I lost very little lean body mass but a significant amount of body fat. For the sake of full disclosure, I was strength training 5-6 days per week and doing absolutely zero steady state cardio which may be a topic in a future post. I’m including this for further support that constant eating is not necessary and personal preference should be the determining factor for each individual’s meal frequency.