Intermittent Fasting

Intermittent fasting (IF) is a diet methodology involving limiting intake of food into short windows during the day. These short fasts typically provide a window of six or so hours per day that the participant can consume their daily intake of food, but there are many strategies of fasting to fit varied lifestyles and goals. As with any healthy diet, the general mission is reducing overall intake of calories to facilitate weight loss and overall well-being.

So how does the process work?

As we consume food, nutrients are broken down by body’s enzymes in the gastrointestinal system and result in a supply of various molecules in the bloodstream. Carbohydrates and refined grains (flour, rice, etc) break down quickly into sugar, which the cells then utilize for energy. However, unused sugars are quickly converted into fat stores. The key to avoiding this transfer? Exercise and fasting.

Exercise provides a natural use of the body’s glucose as it is released as energy and put to work. Fasting lowers the body’s insulin levels and facilitates a transition to the next source of energy, as sugar is no longer readily available. The source the body turns to is those same fat cells. This evolutionary mechanism of the human body called, gluconeogenesis (or literally “glucose creation”), was a genetic adaptation aimed at providing optimal performance to early humans in times of food shortage.

What is the science behind fasting and how long should you fast?

There are a lot of answers to this one, but we can start by looking strictly at the science. The chart below shows the various stages of the body’s use of insulin and the subsequent transition to using fast stores for energy. (Credit to Idmprogram.com for providing this informative graphic).

1. Feeding – During meals, insulin levels are raised. This allows uptake of glucose into tissues such as the muscle or brain to be used directly for energy. Excess glucose is stored as glycogen in the liver.
2. The post-absorptive phase – 6-24 hours after beginning fasting. Insulin levels start to fall. Breakdown of glycogen releases glucose for energy. Glycogen stores last for roughly 24 hours.
3. Gluconeogenesis – 24 hours to 2 days – The liver manufactures new glucose from amino acids in “gluconeogenesis”. In non-diabetic persons, glucose levels fall but stay within the normal range.
4. Ketosis – 2-3 days after beginning fasting – The low levels of insulin reached during fasting stimulate lipolysis, the breakdown of fat for energy. The storage form of fat, known as triglycerides, is broken into the glycerol backbone and three fatty acid chains. Glycerol is used for gluconeogenesis. Fatty acids may be used for directly for energy by many tissues in the body, but not the brain. Ketone bodies, capable of crossing the blood-brain barrier, are produced from fatty acids for use by the brain. After four days of fasting, approximately 75% of the energy used by the brain is provided by ketones. The two major types of ketones produced are beta hydroxybutyrate and acetoacetate, which can increase over 70-fold during fasting.
5. Protein conservation phase – >5 days – High levels of growth hormone maintain muscle mass and lean tissues. The energy for maintenance of basal metabolism is almost entirely met by the use of free fatty acids and ketones. Increased norepinephrine (adrenalin) levels prevent the decrease in metabolic rate.

The concept of fasting is to lower insulin and allow fat cells to release their stored sugar. This in turn reduces weight as fat cells are depleted. Numerous studies have pointed out the various lengths of time for this insulin drop to occur, but the consensus is it starts to pick up after about 8 hours and accelerates rapidly as you approach and pass the 24-hour mark. Glycogen, or glucose energy stores, lasts around 24 hours before depletion. After this point, almost all energy used is coming from stored fat cells. Absent other health conditions, it is generally safe for the body to endure a fast lasting 24-48 hours, as long as the individual is regularly hydrating with water.

In a recent Harvard study, intermittent fasting was shown to shed weight, reduce blood pressure, cholesterol, and improve blood sugars. Almost all studies performed show that IF is safe and effective. However, it is the timing of the fast and the length that can provide dramatic and sustainable results in weight loss and diabetes prevention. According to Dr. Deborah Wexler, Director of the Massachusetts General Hospital Diabetes Center at Harvard Medical School; “There is evidence to suggest that the circadian rhythm fasting approach, where meals are restricted to an eight to 10-hour period of the daytime, is effective,”

Can you do it?

Most people, when faced with such a proposition, say that they couldn’t imagine going without food for more than 24 hours, or even simply limiting intake to a six-hour window every day.

Personally, I find that a 24 hour fast two or three days per week, is very effective. I find my appetite is suppressed, my energy levels are great, and I experience consistent and sustained weight loss. The best part? I haven’t dramatically changed what I am eating (I try to be healthy of course but it’s not a rule). For those suffering from chronic pain; weight loss, ideal energy levels, and a general avoidance of inflammatory food is even more critical.

The best diet is one that works for you. Make it too hard and you’ll crash and revert, getting rid of any gains and sometimes getting to a worse point than they started with. But with a little training (it’s more brain than body), anyone can implement intermittent or extended fasting with success.

Some closing tips

1. Avoid sugars and refined grains. Instead, eat fruits, vegetables, beans, lentils, whole grains, lean proteins, and healthy fats (a sensible, plant-based, Mediterranean-style diet).
2. Let your body burn fat between meals. Don’t snack. Be active throughout your day. Build muscle tone.
3. Consider a simple form of intermittent fasting. Limit the hours of the day when you eat, and for best effect, make it earlier in the day (between 7 am to 3 pm, or even 10 am to 6 pm, but definitely not in the evening before bed).
4. Avoid snacking or eating at nighttime, all the time.

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