The basics of losing weight are fairly simple and can be summed up in one simple phrase: eat less, move more. If you do nothing but take the advice found in that phrase, you will lose weight. Unfortunately, some people take that advice to an extreme and suffer some unforeseen consequences. Your body enters what is commonly referred to as "starvation mode" when you don't eat enough which can cause slower than expected weight loss and plateaus.
Losing Weight 101
Your body uses a certain amount of energy each day. We get all the energy we need from food. When we take in either more or less energy (food) than the body uses each day, our weight changes (increases or decreases). For example, an average man needs about 2,500 calories per day to maintain his weight (use the calorie calculator to figure out how much food you need to maintain your own weight). If he were to eat 3,000 calories in a day, the body would have to deal with a calorie surplus (too much energy) of 500 calories (the body would need to find something to do with the extra 500 calories coming in from the diet). The way the body deals with a surplus is by storing that extra energy as fat causing weight gain.
If that same man were to eat 2,000 calories in a day, the body would now have to deal with a calorie deficit (not enough energy) of 500 calories (the body would need to find non-food sources to make up for the shortfall of 500 calories coming in from your diet). The body deals with a calorie deficit by drawing on fat stores for energy causing weight loss.
If you want to lose weight, all you need to do is bring the level of your food intake under your level of energy use. Consistently eating less calories than your body burns will force your body to draw upon fat stores for energy causing weight loss. You have two opportunities to influence this energy balance equation: food and energy use.
In addition to eating less, you can also expend more energy (exercise) which will widen the gap between how many calories you burn and eat. This balanced approach of eating less AND moving more will yield the best, healthiest and longest lasting result. Problems arise with weight loss strategies when dieters rely too much on cutting calories rather than also exercising more.
Your metabolism can be described as the sum of all the energy needs in the body. Your body needs energy to digest & absorb food, support the brain, heart, liver, kidneys and other organs, repair damaged tissue and move around (physical activity). Even without exercise, your body still has a need for energy to simply keep you alive. Your metabolism or daily energy needs are not set in stone. Instead, your metabolism is fluid and can speed up or slow down based on inputs such as amount of food eaten and exercise performed.
The amount of food you eat can affect your metabolism. Our body has built in protection from prolonged periods of reduced calorie intake (starvation). Easy to find food such as grocery stores and fast food restaurants were not always widely available. Back when our ancestors used to hunt and gather food, they would go long periods of time with little energy intake. To help us survive, our metabolism would slow down in order to conserve the little energy we had left. This can be compared to driving slower when you're almost out of gas and unsure the distance to the next gas station.
Today, this starvation mode kicks in when your calorie intake drops too drastically. If your body needs 2,500 calories per day (to maintain weight) and you start eating 1,000 calories per day, you would expect your calorie deficit to be 1,500 calories leading to substantial weight loss. The problem is that if you cut your calorie intake to 1,500 below what you burn, your metabolism would slow (starvation mode) and burn a lot less than 2,500 calories. Your calorie deficit would turn out to be a lot smaller than 1,500 calories.
Diet vs Exercise for Weight Loss
Cutting your calorie intake drastically is a bad weight loss strategy for a number of reasons. Most importantly, cutting calories very drastically is not sustainable. The changes you need to make to cut 1,000 or more calories from your daily intake is too much for you to handle. Taking this path might last a few days or even a few weeks but eventually, your diet will prove too much and the changes you have made will lead to a failed diet. Once you go back to your old ways, the weight will come right back on.
Another reason that a drastic calorie cut is a bad idea is nutrient intake. Your body needs a certain amount of vitamins and minerals each day to support normal bodily functions including energy metabolism, immune function and tissue repair. The typical American diet is already deficient in many nutrients. Eating less will further decrease your intake which can lead to some inconvenient if not serious health issues. Slower, more sustainable weight loss options that include exercise will lead to healthier and more long lasting results.
Remember that the weight loss equation has two parts that you can manipulate to lose weight: diet and exercise. Combining diet and exercise will allow you to lose weight without making huge changes. You must create a calorie deficit to lose weight. You can create a calorie deficit by either eating less, exercising more or combining both.
Losing weight by moderately cutting your calorie intake and increasing your physical activity will yield the best results. Moderately cutting your calorie intake will not have the same negative consequences (starvation mode) involved in drastically cutting your calories. While cutting calories can negatively impact your metabolism, increasing your physical activity level can do the opposite.
Exercising burns calories because moving requires energy. The more you move, the more calories you burn. In addition to the calories you burn while exercising, your metabolism is also increased for 24-48 hours after you stop exercising. Physical activity speeds up your metabolism even after you stop exercising due to the recovery phase of exercise. The recovery phase of exercise involves repairing damage sustained to the muscle fibers while working out and replenishing energy stores used up during exercise. All of this burns calories. Exercising also builds muscle. Because muscle requires energy to maintain, the more muscle you have, the more calories you burn, even at rest. A 200 pound person that is made up of 10% body fat will burn more calories throughout the day than a 200 pound person that is made up of 25% body fat.
The Bottom Line - Solution to Starvation Mode
The solution to starvation mode and weight loss plateaus is to take a balanced approach to weight loss that includes both diet and exercise. Increasing your physical activity level will speed up your metabolism enough to counteract any slight decrease caused by a MODERATE decrease in calorie intake. Taking this balanced approach will yield healthier, more long lasting and easier results.