I’m Dr. Emily Dhurandhar. I have studied the science behind weight loss for the last 18 years. I have also taught about obesity and nutrition at several universities. During these experiences, I have noticed there are a lot of misunderstandings about how weight loss works.
Understanding how weight loss works will help any effort to lose body fat. When losing weight, the real objective is losing body fat. Weight loss is just an approximate marker for fat loss. With a better understanding of fat loss, it becomes possible to filter through all the advice on fat loss that is everywhere. Time and efforts can be spent more wisely, through a better understanding. And you will be more likely to achieve your goals.
The fundamentals
What is fat?
Fat tissue is the body tissue underneath your skin and in your belly that you see as “fat”. The fat cells in that tissue store energy, like a gas tank stores petrol. But instead of petrol, fatty acids are kept in your fat tissue. Fatty acids are long, compact carbon chains that the body can break down to make energy.
Why does the body burn fat?
The body burns fat to make energy for to maintain itself, and for movement and activities.
Our bodies use something called adenosine triphosphate (ATP) for energy. “Fat burning” is really just breaking down fat to make ATP for energy. Carbohydrate and protein also contain energy because they can also be broken down to make ATP in different situations.
When does the body burn fat?
All the time! When sleeping, sitting still, resting, and during light exercise, fat is the preferred source of energy by most tissues in the body. It can also make energy from protein and carbohydrate, but neither of those is the “go-to” fuel source for the most common activities that we spend the majority of our time doing.
When does the body store fat?
The body puts fat away after meals. That is when fat is digested and absorbed. But not all of the fat that you eat will be stored right away!
Sometimes, your body will use the fat you just ate for energy right away. But if it is not needed right away, that’s when it will be stored for later. If more carbohydrate or protein has been consumed in a meal than your body needs right away, that can be converted to fat and stored.
You may now be asking- if we store some fat every time we eat, why don’t we gain fat every time we eat? That is because the fat we use in a day is about equal to the fat we store in the body every day. So the net difference across the day is zero. That is why fat stores stay about the same, from day to day, when we are in a healthy state.
And, that is why only a major disruption in the amount of fat coming in vs. the amount being burned is the only way to cause fat loss.
What makes fat loss happen?
Normally, a healthy person eats the same amount of energy that they use each day. Any fat that gets burned gets replaced almost immediately. This is pretty well regulated by your body, and happens automatically.
To make the body lose fat, more calories must be burned by your body than what is consumed in the diet. The fat burned will not be replaced by the diet, and fat loss will happen. This state is called “negative energy balance,” because the body is at a net loss for energy.
How to create negative energy balance
Eating less food is the most effective way to create negative energy balance. That way, the body is consuming fewer calories than it burns. Fat becomes the main source of energy to burn first, and it gets used up. At least in theory, it is that simple.
But in practice, it is not so simple. Here is why.
Losing Weight is A Battle with the Body
Losing weight isn’t a normal, natural process. To understand why, take a deeper dive into an extreme example. We have already talked about how eating less causes weight loss. Then let’s answer this question: if someone were to stop eating, would they eventually disappear into thin air?
No! Of course not. When people fast or endure a famine, they become thinner and smaller. But they do not just disappear. Because survival depends on having a working body for as long as possible. If there was no swift and extreme adaptive response to starvation, no one would survive for very long.
And in fact, we do see a response to even a more moderate form of starvation, such as a weight loss diet. When weight starts to drop because of an intentional reduction in food intake, the body fights back. Hunger, mood changes, head aches, and fatigue are common. Even the energy expended to maintain the body decreases, as the body becomes more efficient to conserve energy and mass.
These side effects of weight loss make it a battle. But, these side effects can and should be managed. A diet that is higher in protein and fiber is one strategy that can help. Both nutrients can lessen the side effects of weight loss and make it more tolerable.
Getting Enough Nourishment
Another challenge when going into negative energy balance to lose weight is giving the body enough nourishment. There are 40 essential nutrients that are needed for survival. Eating less food, while still getting enough of those essential nutrients, requires some nutrition knowledge and skill.
This is complicated by certain conditions that require special attention to specific nutrients. For example, if someone has low bone density and is at risk of osteoporosis, the diet needs to be sufficient in Calcium and Vitamin D. So that individual needs to take less food, but without taking less of the foods with Calcium and Vitamin D.
Another challenge is reducing food intake in the right amounts from one food group to the next. Some nutrients are only present in certain foods. So if that food or group of foods is cut from the diet, that can lead to a deficiency of that nutrient. And nutrient deficiencies can worsen your health.
Consistency and Control
The final challenge of going into negative energy balance and fat loss is consistency. Losing body fat requires a consistent reduction in calorie intake, week after week. But there are some days or weeks where that seems impossible. For example, weddings, vacations, and other life events often involve food-related traditions. There are times when you just cannot control what food you are eating.
There are also challenges to knowing how many calories you eat on a daily basis. Perhaps someone cooks for you, and you aren’t sure what is going into your food. Or, maybe you have a fast-paced lifestyle that relies on restaurant food.
Maintaining some consistency in controlling your food intake requires a special effort and sacrifice. There will be setbacks, and it is important not to be discouraged by those setbacks. Remember, even if it doesn’t go perfectly all the time, everyone trying to mind their calorie intake is still doing better than if they weren’t paying any attention at all! And even 80-90% of consistency for six months will give you a lot more benefit than perfect consistently for just a week or two.
