What if I told you that all you need to do to lose weight is read a calendar and tell the time? These are the basics for successfully following an intermittent fasting regimen.
Can it be that simple, though? Does it work? And what is the scientific basis of fasting? As a dietitian and expert in human nutrition and metabolismI am frequently asked such questions.
Simply put, intermittent fasting is defined by alternating defined fasting periods with periods during which eating is permitted. A method is two day fast. On “fasting days”, followers of this form of fasting are limited to consuming no more than 500 calories per day; on “feast days”, which occur every other day, they can eat freely, with no restrictions on the types or amounts of food eaten.
Other methods include the increasingly popular method Method 5:2. This form of fasting involves five days of feasting and two days of fasting per week.
Another variant is based on a time-limited diet. This means that followers must fast for a specified number of hours – usually 16 to 20 per day – while freely consuming food within a designated period of four to eight hours.
To answer these questions, it helps to understand the basics of human metabolism.
Human Metabolism 101
The human body needs a continuous supply of energy to sustain life, and the foods we eat provide us with this energy. But because eating is often followed by periods without eating, a complex set of biological pathways are in place to meet the body’s energy needs between meals.
Most pathways operate at a certain level all the time, but fluctuate after a meal in a predictable pattern called the fed-quick cycle. Cycle times can vary depending on the types of foods eaten, the size of the meal, and the person’s activity level.
So what happens, metabolically speaking, after you eat? Consuming carbohydrates and fats leads to an increase in blood sugar and also lipid levelwhich include cholesterol and triglycerides.
This triggers the release of insulin from the pancreas. Insulin helps tissues throughout the body absorb glucose and lipids, which provide tissues with energy.
Once energy needs are met, the remaining glucose is stored in the liver and skeletal muscle in a condensed form called glycogen. When glycogen stores are full, excess glucose turns into fatty acids and is stored in fatty tissue.
About three to 6 p.m. after a meal – again, depending on the person’s activity level and the size of the meal – the amount of blood glucose and circulating lipids return to baseline levels. Thus, the tissues must then rely on fuel sources already present in the body, namely glycogen and fat. A hormone called glucagon, secreted by the pancreas, helps facilitate the breakdown of glycogen and fats to provide the body with energy between meals.
Glucagon also initiates a process called gluconeogenesis, which is the synthesis of glucose from non-food sources. This helps to maintain the correct level of blood sugar.
When the body reaches a true fasting state – around 18 hours to two days without supplemental food intake – the body’s glycogen stores are depleted and tissues like the heart and skeletal muscle begin to rely heavily on fat for energy. This means an increase in the breakdown of stored fat.
“Oh! you might say. “So intermittent fasting is the key to ultimate fat burning?” Well, it’s not that simple. Let’s review what happens next.
The state of starvation
Although many tissues adapt to using fat for energy, the brain and red blood cells need a continuous supply of glucose. But when glucose is not available due to fasting, the body begins to break down its own proteins and converts them to glucose instead. However, because protein is also essential for supporting essential bodily functions, this is not a sustainable process.
When the body enters the starvation state, the body goes into self-preservation mode and a metabolic shift occurs in an effort to spare body protein. The body continues to synthesize glucose for cells and tissues that absolutely need it, but the breakdown of stored fat also increases to provide energy to tissues such as skeletal muscle, heart, liver and kidneys.
This too promotes ketogenesis, or the formation of ketone bodies – molecules produced in the liver as a source of energy when glucose is not available. In the starvation state, ketone bodies are important energy sources because the body is not able to use fat alone for energy. That’s why it’s inaccurate when some proponents of intermittent fasting claim that fasting is a way to “just burn fat” — it’s not biologically possible.
What happens when you break the fast? The cycle begins again. Blood sugar and lipids return to basal levels and energy levels in the body are maintained seamlessly by switching from one metabolic pathway to another previously described. The good thing is that we don’t even have to think about it. The body is well equipped to adapt between periods of feasting and fasting.
If an “all or nothing” diet approach to weight loss sounds appealing to you, chances are it will work. Indeed, intermittent fasting regimens have produced clinically significant amounts of weight loss. Intermittent fasting can also reduce the risk of disease lowering blood pressure and blood lipid levels.
On the other hand, numerous studies have shown that weight reduction from intermittent fasting diets is no bigger than weight loss with a standard low calorie diet.
In fact, the weight loss caused by intermittent fasting is not due to spending time in some sort of magical metabolic window, but rather a reduction in overall calorie consumption. On holidays, dieters generally do not fully offset for lack of food on fasting days. This is what leads to mild to moderate weight loss. About 75% of weight is fat; the rest is lean mass. It’s about same ratio as a standard low calorie diet.
If you still want to pursue intermittent fasting, there are a few things to keep in mind. First, there are no studies on the long-term safety and effectiveness of this type of diet. Second, studies show that intermittent fasters do not consume enough certain nutrients.
Exercise is something else to consider. It helps preserve lean muscle mass and may also contribute to increased weight loss and long-term weight maintenance. This is important because nearly a quarter of the weight lost on any diet is muscle tissue, and intermittent fasting has been shown to be effective for weight loss. for short periods only.
Also, once you stop following an intermittent fasting diet, you will most likely gain weight back. This is a key consideration, as many people find the diet difficult to follow long term. Imagine the challenge of planning six months of feasting and fasting around dinners, vacations and family celebrations. So imagine doing it all your life.
Ultimately, the best approach is to follow a diet that meets current dietary recommendations and fits into your lifestyle.
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