In this interesting study – beef was eaten with either saturated fat from dairy or monounsaturated fat, in the context of a low carb diet. Blood lipids were measured to see what difference the fat type made.
In nutrition studies we used to hear all about saturated fat, and the positive effect of low saturated fat diets on cholesterol levels. Times are a-changing. There are a growing number of researchers who are looking beyond total and low density lipoprotein cholesterol (LDL). It is increasingly recognised that LDL by itself is a poor predictor of cardiovascular disease (CVD) risk. There are many people who get heart attacks who have normal LDL.
The focus for these researchers is on atherogenic dyslipidemia. What is this – you are probably asking? Atherogenic – ” Refers to the ability to initiate or accelerate atherogenesis—the deposition of atheromas, lipids, and calcium in the arterial lumen” or simply – clogging your arteries. Dyslipidemia – an abnormal cholesterol profile. Atherogenic dyslipidemia is a cholesterol pattern that leads to atherosclerosis. It is characterised by a particular triad: elevated triglycerides (TG), reduced High density lipoprotein (HDL) often called ‘good cholesterol’, and increased levels of small LDL particles.
LDL is made in different sizes. LDL is a transporter of fats (triglycerides and cholesterol) in the blood stream. Small dense LDL particles carry less lipids. The small size leads to a number of problems which are thought to contribute to atherosclerosis. They are more susceptible to oxidation and are pro-inflammatory to vascular endothelium. They bind more tightly to arterial proteoglycans and penetrate into the arterial wall more easily. They also have a lower affinity for the LDL receptor than larger LDL. As a result they stay longer in circulation, which gives them more potential to oxidse and increase atherosclerotic damage.
LDL normally binds to the LDL receptors on the cell surface, and then gets taken onto cells, so removing the LDL from the bloodstream. Here is a diagram of the LDL being taken inside a cell, the LDL particle is broken down into cholesterol and amino acids.
Confused? Here is a great little animated clip of an LDL particle connecting with an LDL receptor and being taken into a cell. LDL Receptor pathway
Anyhow – back to the influence of diet on LDL particle size. A number of studies show that the best way to influence this antherogenic triad is a reduced carbohydrate diet. This is so even if the diet is high in saturated fat. This 6 week study [Limited Effect of Dietary Saturated Fat on Plasma Saturated Fat] compared two low carbohydrate diets, one high in unsaturated fat, and one in saturated fat. 12% calories as carbohydrates, 29% as protein and 57% from fat.
In both diets TG reduced: by 39%, in SFA, and 34% in UFAdiet. HDL increased by 14% in SFA and 8% in UFA. LDL increased in both 21% in SFA and 9% in UFA diet. However the HDL: LDL ratio remained almost unchanged from baseline in both. What did improve on both diets was the LDL particle size – which increased the same amount (this is good, we want large LDL).
Back to the beef study – it was done to see if beef protein influenced lipid measurements when it was eaten as part of a low carbohydrate diet. The study really compares saturated fat plus beef, with monounsaturated fat plus beef, and the resulting changes in lipids. The diet contained 31%E carbohydrates, 31%E protein, and 38%E as fat, either 8% sat fat or 15% sat fat.The participants previously ate a higher carbohydrate diet (50%E carbohydrate)
Previous studies have shown that multiple features of atherogenic dyslipidemia are improved by replacement of dietary carbohydrate with mixed sources of protein and that these lipid and lipoprotein changes are independent of dietary saturated fat content. Because epidemiological evidence suggests that red meat intake may adversely affect cardiovascular disease risk, we tested the effects of replacing dietary carbohydrate with beef protein in the context of high- vs. low-saturated fat intake in 40 healthy men. After a 3-wk baseline diet [50% daily energy (E) as carbohydrate, 13% E as protein, 15% E as saturated fat], participants consumed for 3 wk each in a randomized crossover design two highbeef diets in which protein replaced carbohydrate (31% E as carbohydrate, 31% E as protein, with 10% E as beef protein).
The high-beef diets differed in saturated fat content (8% E vs. 15% E with exchange of saturated for monounsaturated fat). Two-week washout periods were included following the baseline diet period and between the randomized diets periods. Plasma TG concentrations were reduced after the 2 lower carbohydrate dietary periods relative to after the baseline diet period and these reductions were independent of saturated fat intake. Plasma total, LDL, and non-HDL cholesterol as well as apoB concentrations were lower after the low-carbohydrate, low-saturated fat diet period than after the low-carbohydrate, high-saturated fat diet period. Given our previous observations with mixed protein diets, the present findings raise the possibility that dietary protein source may modify the effects of saturated fat on atherogenic lipoproteins.
The actual changes – very small LDL fell 10% on low SFA diet and 2% on high SFA diet. Phenotype B LDL fell only on the low SFA diet. Total LDL increased on the SFA diet and fell on the low SFA diet. Non HDL-C fell significantly on the low SFA diet: 3.42 to 2.98, and to 3.37 on the high SFA diet. (HDL fell very slighty on the low SFA diet, but not on the high SFA diet)
So what to make of this? If you are eating beef – have it with olive oil? If you are eating butter – don’t eat it with beef – choose another protein?
Perhaps this study points to why red meat (and possibly particularly beef) is linked in epidemiological studies to a greater risk of heart disease.
From the article:
Hence, the present findings suggest an interaction between saturated fat and one or more nonfat components of beef on lipoprotein metabolism. Because there is little evidence for a major role of dietary protein composition on lipoprotein metabolism, this interaction is not likely to be caused by specific amino acids within beef protein. However, saturated fat might be interacting with a micronutrient or other component that is more abundant in beef than in other food protein sources. For example, systemic iron stores have been associated with altered lipid metabolism and there is evidence that heme iron absorption is substantially increased by saturated fat and, in particular, stearic acid, which is abundant in dairy fat.
An interesting study, showing an interaction between 2 foods that was unexpected given earlier studies showing a much smaller difference in the effect of fat types on lipid profiles, in the context of a low carbohydrate diets.