Deficit Diet Dos and Don’ts

#1 Don’t worry about the laws of physics

Nearly every article I read here about weight loss confidently states something along the lines of “to lose weight, you need to be in a calorie deficit.” While this is correct, the way most authors suggest achieving the deficit they say you need is completely wrong.

First, some background.

Energy

We need energy to stay alive and we get that energy from the food we eat. We don’t use the energy found in the food directly, though. The food we eat gets broken down into basic nutrients — like glucose (from carbohydrates), amino acids (proteins) and fatty acids (fats). Amino acids tend to be used to build or repair things in the body and tend not to be used by the body for energy — so we will ignore them in this discussion.

The human body doesn’t directly use glucose or fatty acids for energy, either. This nutrient energy needs to be converted into a chemical energy the body can use — this chemical energy is called adenosine triphosphate (ATP). Our cells use ATP to do the work that helps keep us alive. Little transformers in each cell, called mitochondria, take in nutrient energy and convert it into ATP.

The amount of ATP a person needs depends on several factors including how much there is of that person and how active that person is. The amount needed if a person were to simply lay in bed all day is referred to as their basal metabolic rate (BMR) and when you add in the energy needed for all the activity that person does in a day, it’s referred to as Total Daily Energy Expenditure, or TDEE. BMR and TDEE are typically described in terms of calories.

Deficit Diet Definition

A “deficit diet” is defined as one in which the dieter eats fewer calories than their TDEE would indicate. Given my age, weight, height, and activity level, my TDEE is 2,387 calories. Most nutritionists and fitness instructors suggest about a 15% deficit if I were looking to lose weight — so, for me, that would mean I should eat about 2,029 calories per day (15% less than 2,387). In other words, I should cut 358 calories from my diet each day.

Another way to achieve this deficit — according to those who recommend deficit diets — would be to increase activity by 358 calories. So, if I eat 2,387 calories but expend 2,745 (most of that coming from my BMR) I will achieve the 358-calorie deficit.

In practice, it is typically recommended that we do a combination of both eating a bit less and moving a bit more to create the targeted deficit.

The above is the basic concept behind the “eat less/move more” approach that doctors, nutritionists, and fitness instructors have been recommending for decades. What’s interesting to note is that while this has been the dominant recommendation, the rate of overweight and obesity in the US and many countries around the world has continued to climb.

So, what’s going on — why are people still becoming overweight and obese if the solution is as easy as eating less and/or moving more? Are people just not following the advice or are other factors at play?

#1 DON’T Worry About the Laws of Physics

Those who continue to push the eat less/move more approach like to point out that the First Law of Thermodynamics must be upheld. They figure your body is holding onto energy — if you use more energy than you take in, your body will pull the difference from stored energy (i.e., body fat). And this would likely hold true if the body was a simple machine. The human body, however, is anything but a simple machine. Of course, the Laws of Physics still apply. It’s just that the body has ways to defend against an energy deficit that work within the bounds of these laws.

The human body has many “systems” that run in the background over which we have little, if any, conscious control. One of these systems manages our energy. This system evolved millions of years ago in a food environment vastly different from what we have today. As you can probably guess, the main goal of this system is to keep us from running out of energy — because if we run out of energy, we die. When we take on an energy deficit diet, our “energy-management system” responds in primarily two ways.

Plan A is to motivate us to take in more energy. This is easy for the body to do — it simply releases more of a hormone called ghrelin, which is what causes us to experience hunger pangs. Millennia ago, this would get our ancient ancestors to look for more food — which largely consisted of carrion (leftover parts of an animal killed by some other beast). As far as paleontologists can tell, our ancient ancestors were pretty lean — like the people in hunter-gatherer communities that haven’t been exposed to our Western Diet.

But most of us live in a different food environment now, and we gain more fat than we’d like. When we want to lose some of that fat, we ignore those hunger pangs in the hope that our body will use the excess to keep us going. And this does work, for a while.

Plan B: Remember, our energy-management system is trying to keep us alive. If it senses that we are not taking in more energy like it advised, it responds. Millennia ago, this meant there was no extra food to be had. Plan B, then, is to slow down our metabolism (the rate at which we use energy) to match what we are taking in, or, to even use less than we are taking in, so we replenish the energy that was lost while we were ignoring Plan A. This is why, when on a deficit diet, our weight loss will stall and then reverse.

The eat less/move more approach doesn’t work because it is attempting to beat a system that evolved over two million years ago to keep us alive.

How then do we lose weight?

#2 DO Let Your Body Do the Work

Most people don’t realize that the body has a way to rid itself of excess body fat. It’s part of the energy-management system that doesn’t operate often in our current food environment because high levels of serum insulin (caused by high levels of dietary carbohydrate) inhibit the process. But if you eat a very-low-carb diet, something interesting happens.

The USDA’s Dietary Guidelines for Americans (what had been expressed as the Food Pyramid, and now as MyPlate) recommends we get about 60% of our daily calories from carbohydrate — that works out to about 300 grams of carbohydrate per day. Compare that to what the USDA acknowledges as the minimum daily requirement for carbohydrate: “The lower limit of dietary carbohydrate apparently is zero, provided that adequate amounts of protein and fat are consumed.” [Taken from the USDA’s 2005 Panel on Macronutrients: Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids.] One doesn’t need to cut dietary carbohydrate completely out of the diet, but 300+ grams per day tends to interfere with the energy-management system — at least in most people.

If you have excess body fat — as defined by your body’s energy management system, not society or even your conscious self — and you eat very little carbohydrate, something changes in your fat cells. And it is this change that results in the body setting up its own energy deficit. What follows are the details.

Recall the little transformers we have in every cell of our body (except for red blood cells) that generate ATP from the nutrients we eat. When they are using glucose to make ATP, they are very efficient — they make only the amount of ATP their cell needs to do its work. This efficient operation of mitochondria is called “coupled metabolism.” It’s coupled in the sense that the amount of ATP produced is linked to the amount of ATP needed.

When fat cell mitochondria use ketone bodies to make ATP, they become inefficient, and metabolism becomes “uncoupled.” When this happens, the mitochondria waste nutrient energy (ketone bodies) and make more ATP than the cell needs. Ketone bodies are derived from fat — so wasting ketone bodies is, essentially, wasting fat.

So, what we have is a situation where the body is producing more energy than it needs — and more than you are eating. From this perspective, you have that energy deficit: you are eating less energy than your body is putting out. But this accounting deficit is due to more going out, not less coming in. Because the body itself initiates this metabolic uncoupling, it doesn’t get defended like when you eat less than you need or make your body move more than usual.

It’s important to note, however, that you won’t lose body fat forever. Your energy-management system, like most systems in the body, has a normal operating range in terms of stored energy (fat). When your body fat reaches this range, this uncoupled metabolism stops — even if you stay on a very-low-carb diet. This is why you might not be able to lose as much body fat as your conscious self wants. Again, it comes down to hormones — likely the strength of leptin signals from fat cells.

To summarize, imposed energy deficits like eating less and/or moving more get defended by the body and typically don’t work for long-term loss of body fat. What does work for long-term fat loss is a diet that triggers a natural, inefficient use of excess body fat.

If you want to see how a keto (or very-low-carb) diet can take excess fat loss even further, check out this article:

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