Intermittent fasting or time restrictive feeding can be a valuable tool for weight loss and weight management.
**A warning. This in NOT medical advice. If you are diabetic or have pre-diabetes you should consult your physician prior to attempting any dietary change that will change your carbohydrate consumption. Pregnant women and children have not been studied with fasting techniques and should not go on fasting regiments without physician guidance. **
Intermittent fasting or time restrictive feeding can be a valuable tool for weight loss and weight management. The hormonal effects of fasting are so powerful that they can improve or reverse metabolic conditions such as high blood pressure, gout, high cholesterol and type 2 diabetes!
There is even evidence to support fasting as a therapy for inflammatory diseases such as rheumatoid arthritis, neurodegenerative diseases such as Alzheimer’s and multiple sclerosis as well as cancer. There is also compelling evidence that it can extend your lifespan.
There has been increasing chatter over the last several years regarding the topic and many books are available that deep dive into the proven and possible benefits of fasting. This addition to the research corner is meant as a brief summary to review some of the science behind fasting.
Fasting for the purposes of this blog and for PHD clients is defined as the willful abstention of eating for a defined period of time. Fasting is not starvation! Starvation is forced abstention from sustenance with no clear timeline on when it may end or at what frequency you may be able to eat.
Intermittent fasting refers to a specific style of eating based off of the amount of time you are choosing not to eat. There are numerous variations to explore but in its simplest form abstention from food should be accompanied by non-nutritive fluids such as water, sparkling water, coffee or tea.
The term intermittent fasting may be used interchangeably with the term “time restrictive feeding” but some would argue the former is for periods of time longer than 24 hours and the latter is for less than 24 hours. Regardless of what you call it abstaining from food intake has some remarkable effects on the body that are not immediately intuitive, so let’s dig into the science.
The metabolism can be a very confusing and complicated topic, but energy production and consumption can be divided into two distinct simple paths. Feeding and fasting. Consuming food and not consuming food. While fasting is a buzz word today the idea is not new. It is as natural as sleep and our bodies have adapted to accommodate both short and long fasts.
If the idea of fasting provokes fear and anxiety, be reassured that your body is already fasting every day. You likely fast every night when you sleep. In fact, the term breakfast is literally “breaking” your overnight “fast” and intermittent fasting is simply extending that overnight fast.
When you begin to fast, a few things happen in the first few hours. One of the first things that occurs is that your blood sugar starts to come down from your previous meal which begins signaling in your body to adapt.
The subtle hypoglycemia associated with the metabolic shift to fasting results in a shift from burning sugar for fuel to burning fat. It is likely the fastest way to encourage your fat cells to release their energy. The response is driven by two hormonal shifts, a reduction in insulin and an increase in norepinephrine and epinephrine. This study demonstrates a 57% decrease in fasting insulin levels with alternate day fasting.
This reduction is what allows for the reversal of insulin resistance metabolic diseases of obesity such as high blood pressure, high cholesterol, gout and diabetes. Fat cells (adipocytes) cannot metabolize stored fat without a reduction in fasting insulin! This is a key component of failure for weight loss approaches that don’t cause this reduction of insulin in some way! The second hormonal shift, increased epinephrine and norepinephrine, sets fasting apart from a ketogenic diet. The increase in these hormones may produce an even more powerful effect on fat cells than the reduction of insulin as demonstrated in this 2006 study.
Once the metabolic shift has been made and your fat cells are allowed to burn fat two fuel sources are created from the stores. Fat, which is stored as a triglyceride, is broken down into fatty acids and a glycerol molecule. The fatty acids are used to create a fuel that’s name has been popularized to an even greater extent than fasting, ketones.
Production of ketones is completely natural and the desired goal of fasting and “keto” diets. The fuel source is simply the natural product of burning fat and nearly every tissue in your body has the ability to burn ketones for fuel. There is debate on which tissues cannot use ketones but for any that need glucose exclusively the glycerol that is removed from the fatty acids can be converted to glucose as needed. This was famously described by Dr. Cahill in the seminal 1970 paper Starvation in Man .
The process of converting to burning fat generally starts after 8-12 hours which is why fasting needs to occur for longer than this time frame to experience the myriad benefits. While some view ketones as an “alternative fuel source” to glucose research would indicate that it is not only a well-adapted system it may be the preferred system for energy. Using ketones for fuel generates fewer by products and creates fuel more efficiently as described in this 2018 review paper. Additionally, unlike glucose, ketones seem to be used by the body as a signaling system to trigger the adaptations that lead to improved health and likely improved longevity.
Numerous studies demonstrate the power of fasting for weight loss. Indeed, the PHD experience supports the notion that fasting can support letting go of weight. However, letting go of weight can occur in many ways and it’s the way that fasting supports letting go of weight that makes it so powerful. As I have published in this blog weight loss efforts with severe calorie restriction and exercise generate remarkable weight loss but at the cost of slowing the basal metabolic rate (BMR).
Even with aggressive exercise protocols to limit losses to BMR these approaches nearly universally result in weight regain. Fasting generates weight loss with not just maintaining the BMR but it can actually increase it. This maintenance of BMR is critical to successful weight maintenance. A maintained or elevated BMR mixed with activity allows for a much more satisfying selection of foods in maintenance than a severely depressed BMR after a severe calorie restriction diet.
When comparing intermittent fasting and chronic calorie restriction head to head as in this study and this one you can see equivalent loss of body weight but a bias toward fat loss in the fasting group and muscle tissue in the calorie restriction group. These studies demonstrate again the reduction in insulin that accompanies fasting which we already explained is required for burning fat. This insulin reduction allowing for fat burn interplays with the maintenance of BMR to support weight maintenance in the long term.
If we look even deeper at the cellular changes that occur in response to fasting you can see reduction in inflammation markers, increases in expression of antioxidant defenses, DNA repair, protein quality control and mitochondrial function. These cellular responses could lead to additional findings which are under investigation including the benefit of intermittent fasting for rheumatoid arthritis, memory function, Multiple Sclerosis, Parkinson’s, Alzheimer’s disease and cancer treatment and prevention.
In conclusion, fasting should not be considered a new fad but a natural part of human history and metabolism that can unlock tools within our cells. We have unknowingly hidden these tools ourselves with nutrition guidelines that have pushed us to be obligate glucose burners.
The above evidence suggests that for weight loss and maintenance fasting can be a powerful approach that will likely encourage success where others have failed. It is not required but if adapted intermittent fasting will likely benefit you in many ways. I encourage you to explore this natural remedy to metabolic disease that is not only free, it will actually save you money.