Post #25: Understanding How Fat Works To Better Manage Weight Loss (or the answer to “Why The $%@! Am I Not Losing Weight And What Can I Do About It?)

May 26th, 2024

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Today’s post (#25) is on a topic that some of us have no issue with and can therefore take for granted while some others face a lot of frustration dealing with. And that is the question of why we can’t seem to get rid of that excess weight in spite of having done everything we could think of doing. 

I want to start with an important clarification: when we say we want to lose weight, we typically mean we want to lose fat, and in the same vein when we say we want to put on weight, we mean we want to put on muscle. I make this point because quite a lot of people end up losing weight in the form of muscle mass or end up gaining weight in the form of fat, neither of which is desirable.

To understand any fat loss interventions better, let’s begin with a simple primer on how fat cells in our bodies work. As you can see in the figure above, our fat cells (I will focus this conversation on white adipose tissue or WAT as opposed to brown adipose tissue or BAT because the former makes up 99% of total fat) have three inputs and one output. If the inputs exceed the output, our fat reserves increase and we put on weight. When the output exceeds the input, we lose fat and therefore lose weight. One subtle point that may be worth making here is how this concept of fat in vs. fat out in the fat cells relates to calories in vs. calories out in the body. Let’s take the case of a person who consumes 1,500 calories of food and burns 2,000 calories in activity everyday. They have a 500 calorie deficit which needs to be accounted for; these 500 calories are provided from the output of the fat cells that were consumed at some point in the past. It is that fat reserve that is being used up to bridge the delta between calories in and calories out and so understanding how and when fat moves in and out of the cells is important to better understand weight gain or loss.

The inputs into the fat cells are in the form of i) triglycerides (henceforth referred to as TG, a term that you have probably seen in your annual blood tests) that come directly from the fats in our foods or ii) from the TG being transported in our bloodstream through the liver to the fat cells and iii) from glucose, that hasn’t been taken up by the rest of our cells, that in the presence of insulin gets stored as fat. For most healthy folks (characterized by good insulin sensitivity showing up as low fasting insulin values), there is very little contribution from glucose and most of it comes from the first two components, while for the insulin resistant individuals (high fasting insulin and pre-diabetic / diabetic folks), all three components bring in fat. 

Note that I use the fasting insulin levels rather than HbA1c to determine healthy insulin sensitive individuals rather than the typical HbA1c and that is because fasting insulin levels are a leading indicator of insulin resistance while HbA1c is a lagging indicator; put another way, an individual could already be well on their way to becoming pre-diabetic and diabetic even if their HbA1c values look reasonable today. The time difference between it showing up in one’s fasting insulin values versus showing up in one’s HbA1c values can be years. Moral of the story? Make sure to measure your fasting insulin in your regular blood tests. 

The single output of the fat cells involves the breakdown of the TG into free fatty acids and glycerol, both of which can serve as a source of energy for the body. This fat output mechanism gets triggered either when one is undergoing fasting and therefore in the absence of glucose it is the fatty acids that serve as the energy source, or when there is some activity or exercise that needs fuel, or when the body undergoes some sort of shock, thereby releasing adrenaline which in turn promotes this breakdown of the TG to provide an instant surge of energy (the oft heard “adrenaline rush”). However, the output is regulated by a few factors including hormonal levels (certain hormones inhibit the breakdown of fats while others accelerate it), sleep quality, etc.

With this as the background, let’s evaluate the two primary weight loss scenarios (I will keep weight gain as a separate post if there is interest in that topic) and what interventions have the highest probability of success in losing weight:

1. If one is highly insulin resistant (high insulin levels as seen in type 2 diabetics, those with hyperinsulinemia or metabolic syndrome), the fat cells will get inputs from all three sources mentioned above (fat from food, fat from liver and the conversion of glucose to TG) while the output from the fat cell is heavily restricted. This means that the fat cells get larger and one puts on weight. In fact, for such a person, even if they do a fast, their background insulin levels remain high because of being insulin resistant and this creates a situation where even though there is fat in the fat cells that can theoretically be used as an energy source, practically the body cannot access it. 

   The weight loss strategy for an individual with these characteristics is to reduce dietary fat (thereby reducing the amount of TG available for storage in fat cells) and can also contribute to a caloric deficit (which promotes the output of the fat cells as an energy source). One should also reduce dietary carbohydrates (which lowers insulin levels thereby ensuring enough output of the fat cells as an energy source remains high, reduces the conversion of carbs into fat inside the fat cells, and can promote the utilization of stored fat since the body needs the stored fat as an energy source in the absence of enough carbs often called ketosis). Note that I have used the word reduce rather than eliminate fats and carbs because an overall balanced diet is critical to overall health.

2. If one isn’t highly insulin resistant and has normal insulin levels, the fat cells will get inputs primarily from only two sources mentioned above (fat from food, fat from liver) while the output from the fat cell flows on demand. When such a person puts on weight, it is relatively easy to fix it through a low carb diet with an occasional fast to further enhance the fat cell output. 

In both of the above scenarios, improved sleep and lower stress levels will also regulate the impact of cortisol and other hormones that may otherwise inhibit the fat cell output. Increasing muscle mass through strength training helps provide additional storage for glucose from carbs and is a very powerful weight management tool.

This post has more theory than I usually like to get into but I hope it made the interventions that much easier to understand. As always, please provide any feedback you may have on whether these concepts are practically actionable and the explanations useful.

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