Low-Fat Diets Paradoxically Increase Triglycerides
Fats in the bloodstream are known as triglycerides. A higher level of triglycerides in the bloodstream can increase the risk for heart disease. High levels of triglycerides are also a very common feature of diabetes and diabetics are up to five times more likely to have heart disease than non-diabetic people.
For many years, an idea has perpetuated that eating fat will cause the level of triglycerides in the blood to increase. However, when we look at the scientific evidence it is clear that this is not the case. In fact, at least eleven dietary trials have found that a low-fat diet causes the level of triglycerides to increase (1-11), and no studies have found that increased dietary fat increases triglycerides.
Initially, this may seem to be a paradox, however, what these and other studies reveal is that dietary fat is not the villain it was once thought to be.
A low-fat diet will inherently involve the consumption of a large amount of carbohydrate. Guidelines from the British Nutrition Foundation actively encourage people to substitute foods that contain fat for foods that are carbohydrate-based. What is often over-looked is the effect that a low-fat / high-carbohydrate diet has on blood glucose levels.
Figure 1 compares the effects that a high carbohydrate diet has on blood glucose levels with the effects of a high protein and fat diet, during a 24 hour period (12, 13). It can be seen that the high carbohydrate diet causes wild fluctuations in blood glucose and much higher levels of blood glucose overall. It is worth pointing out that the carbohydrate content of the high carbohydrate diet used for this analysis was around 55 percent - this may be considerably lower than the carbohydrate content of the diet that many clients may be following.
Why is this so important? Well, high blood glucose is a serious situation that the body has to rectify as a priority. High levels of blood glucose causes circulatory problems and damage to the inside wall of blood vessels. A high level of blood glucose triggers the release of the hormone insulin, which is required to lower blood glucose concentrations.
Insulin enables the body’s cells to use some of the glucose, but if there is too much glucose the excess is converted into fat (triglycerides). This explains why low-fat /high-carbohydrate diets increase blood triglyceride levels.
Low-Fat Diets Lower ‘Good’ Cholesterol
High Density Lipoproteins (HDLs) are commonly known as ‘good’ cholesterol. In fact, HDLs are not really cholesterol. Yes, they contain some cholesterol, but they are more accurately described as a bundle of proteins, fats, cholesterol and vitamins.
The general structure of a lipoprotein is shown in Figure 2. The fact that HDLs carry other molecules and not just cholesterol, brings into question the whole idea of ‘good’ and ‘bad’ cholesterol. Lipoproteins carry a wide range of substances to and from the cells of the body; it is far too simplistic to designate HDLs and LDLs (Low Density Lipoproteins) as good or bad respectively. This is discussed in more detail in my book $29 Billion Reasons to Lie About Cholesterol.
However, assuming that HDLs are ‘good’ cholesterol and a low level of HDLs increases the risk for heart disease, as is purported currently; it is of interest that a low-fat / high carbohydrate diet drastically reduces the level of HDLs.
A large number of dietary trials have confirmed this correlation between a low-fat / high-carbohydrate diet and low levels of so called ‘good’ cholesterol (1,2,4,6,8,9,11,14-16).
This feature of a low-fat diet has been known for some time, but has not been communicated to health professionals or the general public - possibly because there are huge commercial interests in, and profit to be obtained from, the wide range of low-fat foods that are currently heavily promoted.
In reality, the level of HDLs is reduced when the level of triglycerides is high. A low level of HDLs is likely to be part of the overall condition or syndrome rather than being causative in itself.
LDL Particle Size
Another metabolic abnormality that is influenced by diet is related to the actual size of LDL particles (or ‘bad’ cholesterol). This issue is not related to the level or number of LDLs within the bloodstream, but is associated with the diameter of the LDLs that do exist.
The properties of LDLs change considerably as they become smaller in size. Smaller LDLs have very different effects when compared with larger or normal sized LDLs.
When heart disease is present, fat and cholesterol do not simply clog-up the arteries. Rather, tissue damage occurs beneath the inside wall of an artery and a process of inflammation commences. When LDLs are smaller in diameter, it is thought that they can pass through the inside wall of an artery more easily. Smaller LDLs can more easily become oxidised and cause further tissue damage. In fact, there are at least eight different potential mechanisms whereby LDLs can become dangerous when they are reduced in size (17).
It is now widely recognized that smaller LDL particles are associated with a greater risk for heart disease (18-20). By contrast, larger LDLs are associated with a longer life (21).
Interestingly, a diet that is higher in saturated fat actually increases the size of LDL particles (22,23) and a low-fat / high carbohydrate diet leads to a smaller LDL particle size (14,24-26).
Saturated Fat and Cholesterol
There is a misconception that saturated fat in the diet will cause cholesterol levels to increase and in turn, increase the risk for heart disease. This misconception probably started with Dr. Ancel Keys. Dr. Keys tried to show that blood cholesterol levels are high in countries where people eat lots of foods containing saturated fat. In 1958 he described this ‘connection’ by plotting the data for various countries on a graph (27).
However, just in the same way as other published work by Keys, he had omitted critical data from the graph in order to support his idea. It is now well-known within the scientific community that at the time Keys published his paper, data was available for additional countries that did not appear on his graph, and if these countries were included, the data would have shown no connection at all between fat intake and blood cholesterol levels.
The misconception that saturated fat causes cholesterol levels to increase has fueled the popularity of the low-fat diet. However, the fact is that there has never been any convincing evidence to show that saturated fat in the diet increases cholesterol levels.
There is also a distinct lack of evidence to support the idea that cholesterol itself causes heart disease – as have been discussed in other articles.
How Much Carbohydrate?
Armed with the above information, a logical question emerges concerning the optimum carbohydrate intake compared with protein and fat. This, of course, depends entirely upon the individual person. It is not so much a question of too much carbohydrate per se, but more appropriately, too much carbohydrate for the individual person.
Each person has their own optimal macronutrient ratio as a function of their Metabolic Type®, lifestyle, and exercise levels. This can be thought of in the context of a radio dial where each person has to ‘tune-in’ to their own optimal macronutrient ratio. This radio dial analogy is illustrated in Figure 3.
Suffice to say that if a client has the collection of metabolic abnormalities described in the summary box above, we can be quite sure that their carbohydrate consumption is currently too high for them - the reduction of dietary carbohydrate and the addition of an appropriate exercise program can improve these abnormalities significantly.
- Liu, S et al. ”Dietary Glycemic Load assessed by Food-Frequency Questionnaire in Relation to Plasma High-Density-Lipoprotein Cholesterol and Fasting Plasma Triacylglycerols in Postmenopausal Women” American Journal of Clinical Nutrition 2001;73:560-566
- Radhika, G et al. “Dietary Carbohydrates, Glycemic Load and Serum High-Density Lipoprotein Cholesterol Concentrations among South Indian Adults” European Journal of Clinical Nutrition. Advance Online Publication November 7, 2007
- Garg, A, Grundy, SM and Koffler, M “Effect of High Carbohydrate Intake on Hyperglycemia, Islet Function, and Plasma Lipoproteins in NIDDM” Diabetes Care 1992; 15:1572-1580
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- Smith, J., 2009. “$29 Billion Reasons to Lie about Cholesterol: Making Profit by Turning Healthy people into Patients” Troubador, Leicester
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- Keys, A et al. “Lessons from Serum Cholesterol Studies in Japan, Hawaii and Los Angeles” Annals of Internal Medicine 1958; 48:83-94