Fasting, Starvation and Caloric Restriction

By Anthony Smith, PhD., Juvenon Science Advisor
Fasting, Starvation and Caloric RestrictionRecently, conflicting information has emerged on the topic of fasting, starvation and weight gain. On the one hand, there is the ‘starvation myth’ based on the theory that starving oneself to lose weight can cause weight gain. However, on the other hand, there is now compelling new research showing the beneficial effects of caloric restriction, e.g., weight loss, decreased oxidative stress, inflammation, and increased longevity. In this month’s Juvenon Health Journal we will explore this trending topic and what the newest research reveals.

The terms fasting, intermittent fasting, calorie restriction and starvation are often used interchangeably. But are they really different words for the same thing? Yes. And no.

In some sense, these terms are similar and describe aspects of the same thing. If you eat fewer calories than your body ‘burns’ each day, you will lose weight. But the ways and means of fasting, starvation and caloric restriction give rise to vastly different physiologic and metabolic outcomes– hence the confusion.

On the cellular level, the main target of fasting, restriction and starvation is our mitochondria– the tiny metabolic engines that power every cell in our bodies. Mitochondria convert the chemical energy potential in food into electrical and mechanical energy for our bodies. Mitochondria are very dynamic–always changing in size, population and energy potential in relation to our exercise, diet and lifestyle.

Before continuing, let’s look at the subtle, yet important, differences between fasting, calorie restriction and starvation as scientific terms.

Intermittent Fasting
Intermittent fasting (IF) is simply the practice of skipping food intake for specific periods of time, generally 18-36 hours a couple of times per week. Increased food intake may result after periods of IF, so there may be no overall reduction of calories.

Although it has garnered much media attention in recent months, intermittent fasting is by no means a ‘new’ concept. Indeed, intermittent fasting mimics the evolved aspects of our physiology. Think about it this way: Paleolithic man almost certainly did not have access to daily 2,500 calorie diets rich in carbohydrates and fat.

It’s important to point out that intermittent fasting is technically not a form of starvation, which is defined as a temporary state of very low or no caloric intake.

Calorie Restriction
Caloric restriction (CR) refers to long term 30 percent to 60 percent reduction of caloric intake and is generally undertaken in laboratory or research settings.

There is much published research, studying CR in rats, dogs, primates and humans. The key to CR is precise control of food intake and rigid, long term adherence to the CR regimen. CR is a form of mild starvation. Research supports that if you reduce the caloric intake for long periods of time, there will be significant weight loss. A host of other beneficial physiologic and metabolic endpoints are also reported to be improved.

However, reports also revealed that irritability, anxiety and extreme cravings are also characteristic of CR. Therefore, the adaptation of a CR lifestyle outside of research settings seems impractical for all but the most obsessive personalities.

How Crash Diets Fail
From the grapefruit diet to the cabbage soup diet, temporary starvation or crash diets have long been popular with those who yearn to lose weight fast. There is no argument that starvation will result in weight loss. But what happens when we induce a metabolic starvation mode? And why do crash diets fail?

Simply put, temporary starvation slows the metabolism. The basal metabolic rate declines and our physiology slows as well. Not surprisingly, the dieter feels tired, sluggish and cranky.

Here’s what is occurring behind the scenes of that promising new crash diet. Since the body must start consuming its reserve energy (fat), it enters a period of extreme metabolic economy. Since there is a metabolic fuel shortage, mitochondria tend to shrink and go ‘offline’ in the interest of preserving this economy. If you keep to starvation mode, long-term, through ingestion of a very-low calorie diet, the metabolism rebounds and you enter the sort of metabolic state described in CR.

Typically, however, starvation mode ends and food intake is resumed. You might think, ‘hey, that doesn’t sound so bad for a dieter,’ but you’d be wrong and here’s why.

Under the context of starvation induced slow-metabolism, the first priority of our physiology is to restore the reserves that were consumed. So even resuming a ‘normal’ calorie diet after a short period of starvation will result in rapid weight gain. Starvation also puts your health at risk with other possible complications such as vitamin and mineral deficiencies, hormonal imbalance and the potential for psychological and behavioral disorders related to food.

The starved state is characterized by extremely low blood glucose levels. If we have fat reserves, it seems like starvation would be good, right? Well, it’s not so simple. The heart and skeletal muscles are efficient users of mobilized fat energy, but the brain and central nervous system are strict metabolizers of glucose, not fat.

So, during the starved state, the body preferentially focuses its physiology on making glucose for the brain not mobilizing fat for the muscles. This keeps you alive, but muscle metabolism shrinks because mitochondria shrink in size and population. This state is often referred to as a shrunken or slow metabolism and it can have a lasting negative impact on your health. Importantly, the altered metabolism makes it easy to gain weight and hard to lose weight in the future.

How Intermittent Fasting Is Different
Intermittent fasting, as previously mentioned is not technically a form of starvation at all. Almost all mammals who walk the earth today are highly specialized organisms whose metabolic systems are highly adapted to periods of IF.

Despite the common warnings in health and exercise journals that the key to proper health and exercise is constant and regular eating, a vast body of research shows this to be completely erroneous. One or two 24-hour periods per week with no food intake have been shown not only to be safe, but actually beneficial for metabolism and overall health. This is not long enough for your body to enter starvation-mode.

Again, intermittent fasting is not a new concept. It was not until the advent of the industrial revolution and the subsequent creation of the food industry that humans began to eat daily, calorie-rich diets. Along with people started to view IF as a sign of poverty and ill health.

For millennia of human history, our ancestors regularly missed food for short periods and experienced nothing like the sort of metabolic diseases our society suffers from today, e.g., diabetes, obesity, chronic fatigue, etc.

Sensible Weight Loss Strategies
Healthy weight loss can only be accomplished by limiting calories in a sustainable and regular fashion. Proper care of our metabolism is key. Crash diets tout quick and easy weight loss, but the long term effects can be devastating. Induction of starvation-mode metabolism is unhealthy and carries the risk rebound weight gain and more. The type of alterations seen in the mitochondria in response to cycles of starvation and weight gain can be permanent and lead to cardiovascular disease, insulin-insensitivity, chronic fatigue and inflammatory diseases.

In the coming months, Juvenon Health Journal will continue to explore different facets of a healthy, efficient metabolism.