Every time I review someone’s blood test results, and then discuss with them what they mean and what they should do to improve their numbers, there’s something I almost always have to explain. And this was the relationship between fasting insulin and triglyceride levels.

Take a look at this plot:

Plot showing ten pairs of measurements of insulin and triglycerides, made from the same blood samples. They were collected between 2011 and 2017, and all are from my own blood tests.

It shows measurements of insulin concentration on the horizontal axis in mili units per millilitre (mIU/ml), and triglyceride levels on the vertical axis in milligrammes per decilitre (mg/dl). This is a correlation plot in which independent measurements of one variable are plotted against independent measurements of another in an attempt to see if there is a relationship between them.

Is there an order in the way the dots are organized? They are clearly not randomly distributed as a circular cloud of dots—it would mean that there is no relationship. Instead, we see what looks like a linear relationship in which lower values of insulin correspond to lower values of triglycerides, and higher values of insulin correspond to higher values of triglycerides. It’s not a straight line, but it’s definitely a clear linear relationship, and the value of the correlation coefficient, which quantifies how tight the relationship actually is, of just under 0.9 is pretty close to 1. In other words, it’s a pretty tight linear relationship.

Triglyceride is a fancy word for fat or lipid, because fat molecules are composed of three fatty acids held together by a glycerol structure. This is what triglyceride refers to. The amount of fat in the blood is affected by the amount of fat we eat, and the amount of body fat we have. Naturally, after a fatty meal, triglyceride levels will increase as the fat goes from the digestive system into the blood, they will reach a maximum, and then start to go down. The longer we wait before we eat again, the lower they will go. But there’s a few complications.

The first is that depending on the amount of insulin, one of whose jobs it is to transport nutrients into cells, whatever is circulating in the blood—and this includes glucose, of course, but also protein and fat—will in general be stored away faster if insulin is higher, and slower if insulin is lower. This means that if you eat fat together with sugar or starch, the whole lot will be packed away, and mostly as fat, minus the little bit of glucose your muscles and liver have room to store up as glycogen.

The second is that depending on the state of insulin sensitivity—the fundamental parameter that determines how well or poorly cells can use fat for fuel—triglycerides will in general be used up faster if we are more insulin sensitive and slower if we are more insulin resistant. This means that in the morning, twelve to fourteen hours after having had the exact same meal, the more insulin sensitive person will have lower triglyceride levels than the more insulin resistant.

And in fact, no matter if we have a measure of fasting insulin or not, and no matter how little we know about the person’s overall health, fasting triglyceride concentration is probably the best general marker of insulin sensitivity. Nevertheless, because their levels fluctuate quite a lot over the course of each day as a function of what we eat and drink, it is true for triglyceride levels as it is true for many other blood tests that are affected by the kind and amount of food and drink we’ve had over the last days, and most importantly by the amount of sweet or starchy carbohydrates.

Now, take a look at this second plot:

Plot showing, in addition to the 10 points shown in the first plot (in red), another 20 pairs of measurements of insulin and triglycerides, also all from the same blood samples, but from seven other persons.

It shows the same 10 data points shown in the first plot from my own results, but with another 20 pairs of measurements taken from other people that I’ve coached and helped with the interpretation of their results. You can see that the relationship is better defined because of the additional points that now together cover a wider range of values on both axes.

However, you can also see that, the relationship is not as tight. In particular, there are a few points that are quite far off the main trend—mostly those at the top of the plot with high triglyceride and low insulin values. We see how these off-trend points affect the tightness of the relationship seen in the initial data set when we compare the values of the correlation coefficients. These off-trend points lead us to the third complication I wanted to bring up.

But first, please take a minute to consider the matter: What could lead to having low insulin and at the same time high triglycerides? What could be the cause of the difference between my numbers, which did contain some very low insulin levels, but all of which were paired with equally low triglyceride values, and this other person’s numbers? What causes insulin to go down? What happens when insulin is low? What could cause triglycerides to go up while insulin is low?

Insulin, no matter how high it is, will start to go down when we stop eating. The longer we fast, the lower it will go. Each person’s baseline will be a little different depending mainly on their metabolic health and their body fat stores. The more efficient the metabolism is at using fat for fuel—the more insulin sensitive, the lower insulin will go. But also the lower the body fat stores are, the lower insulin will go. On the flip side, the more insulin resistant and the fatter we are, the longer it will take for insulin to drop and the higher it will stay at baseline.

This is pretty shitty. I mean, as we develop insulin resistance, average insulin levels will become higher and higher. As a result we’ll store calories into our growing fat cells more and more easily, and will therefore become fatter and fatter, faster and faster. But fat cells also secrete insulin! So, the more fat cells there are, the higher the insulin levels will be, and the harder it will be to lower our basal insulin. To burn fat, we need to lower insulin levels. The fatter we are, the higher the insulin levels will tend to be. And the fatter we are, the harder it will be to lower insulin levels.

It’s a bit of a catch, but in the end, it’s not such a big deal because basically everyone who is overweight and who starts to fast and restrict carbohydrates melts their fat stores away very well. It works incrementally: insulin goes down a little, insulin resistance is reduced a little, fat-burning starts; insulin goes down a little lower, insulin resistance is further reduced, fat-burning increases; and on it goes, until we have lost all those extra kilos of fat that we were carrying on our body, be it 5, 15, 20, 35, 60 or even 100 kg of fat! It’s just a matter of time.

Now, after this little tangent on insulin and fat stores, we can come back to those anomalous points in the plot, the most conspicuous of which is the one just below 120 mg/dl of triglycerides but only 3 mUI/ml of insulin. Have you come up with an explanation? Here is mine:

That point is from one of my wife’s blood tests. It is unusual because it was done after 24 hours of fasting. My 24-hour fasting blood test done a number of weeks before, and my numbers were 41 for trigs at 2.3 for insulin. The difference between her and I was that I was already very lean, whereas she wasn’t. Therefore, as she fasted, her insulin levels dropped very low, and then the body started releasing its fat stores into the bloodstream in high gear. This is why her triglyceride levels were this high while her insulin was that low. It’s almost certainly the same for the other two points up there with trigs at 110 and 90 with insulin around 4 and 2.5 (the latter one of which is also my wife’s).

Since we did many of our blood tests around the same time, there are 9 data points from her on the plot. Several are in the centre of the main trend at insulin values between 6 and 7, but I’d like draw your attention to her lowest insulin value that was measured at 1.8, and at which time her trigs were at 57, and her lowest triglyceride level of 48, at which time her insulin was at 2.2. This shows that on average her values are a little further along the trend than mine are because of the small difference in body fat, but that she has good insulin sensitivity, and a well-functioning metabolism that can efficiently use fat for fuel.

The other off-trend point, but in the other direction on the right hand side, with insulin just above 10 and trigs around 65, is from my mother’s first blood test which I ordered and included insulin and trigs, before I got her off carbs. She was 82 at the time, eating a regular kind of diet, but not a very nutritious or varied diet with plenty of bread and cheese, because she had serious problems moving around and taking care of herself while still living alone. And so, it’s just the result of being older, having plenty of carbs, but not being highly insulin resistant nor highly overweight. Her baseline insulin levels were just generally higher because of her age and diet, but her trigs weren’t excessively high.

However, after just four days of intermittent fasting on a very low carb regime with most calories coming coconut oil spiked green juices and coconut milk smoothies, her insulin went from 10.3 to 4.7, and she lost 5 kilos, which, of course, were mostly from the release of water that the body was retaining to counter the effects of the chronic inflammation that immediately went down with the very-low carb regime and fasting.

Later, having sustained this strict green healing protocol for about 6 weeks, her numbers were at 2.9 for insulin and 56 for trigs. And by then she had lost another 5 kg, but this was now mostly fat. She had, at that point, recovered full insulin sensitivity, had lost most of her body fat stores, and overhauled her metabolism. She was 83 at that time, which shows that this sort of resetting of the metabolism can work at any age.

On this note, let’s conclude with these take-home messages:

First, the next time you get a blood test, request that insulin and triglycerides be measured, because it’s the only way to know what your fasting insulin actually is, and because it is very telling of your level of insulin resistance or sensitivity, overall metabolic health, as well as your average rate of ageing as we’ve seen in a previous post on insulin and the genetics of longevity.

Second, when you get the results back, you will be able to tell from your triglycerides concentration, in light of your insulin level, either how well the body is using fat for fuel—in the case you are already lean, or how fast you are burning your fat stores—in the case you still have excess body fat to burn through.

And third, resetting metabolic health can be done at any time and at any age, and is yet another thing that shows us how incredible our body is—the more we learn generally or individually, the more amazing it reveals itself to be.

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