There has never been a direct link showing that saturated fat consumption causes heart disease. It is always a two-step process. Consumption of saturated fats raises LDL cholesterol and high LDL cholesterol increases risk for heart disease and stroke.
However, dietary cholesterol actually has very little effect on the cholesterol levels in our blood. Our bodies produce most of the cholesterol we need. Also, as I’ve discussed in previous posts, it’s important to look at particle size and high LDL isn't necessarily a bad thing if the particles are big and buoyant (vs. small, dense particles that stick to your arterial walls!).
A meta-analysis looked at the effect of replacing saturated fats in the diet with polyunsaturated fat, carbohydrates, and monounsaturated fat. Replacing saturated fats with polyunsaturated fats minimally lowers risk for CVD. On the other hand, replacing saturated fat with carbohydrates actually had no benefit on the risk of CVD, and when looking at the pooled analysis of 11 observational cohorts, it actually slightly increased the risk for CVD.
This relates back to the consumption of dairy, because as I stated in my last post, the argument for consuming low-fat dairy products are for better health, especially heart health. But since these low-fat dairy products usually contain added sugar, it actually doesn't provide any extra benefit than just consuming the plain full-fat version! The study also showed that the higher the percentage of calories replaced with saturated fats instead of carbohydrates, the more HDL cholesterol increased! This provides some evidence that low-fat and subsequent high sugar intake in place of full-fat products may not be the best for heart health.
A randomized controlled trial studied the effects of either a very low fat, high unsaturated fat, or very low carb diet containing the same amount of calories on body composition and cardiovascular risk. After 8 weeks of being on the specific diet, researchers found that the very low carb diet resulted in similar fat loss as the diets low in saturated fats. But, the very low carb diets were more effective in improving triglycerides, HDL cholesterol, fasting and postprandial (after-meal) glucose and insulin levels. This provides more evidence that high saturated fat and low carbohydrate intake may not relate to risk factors for cardiometabolic conditions. Although it is hard to ensure compliance on these types of studies, I think the researchers did a very good job by supplying the key foods for each diet to the individuals every two weeks.
A systematic review looked at 16 studies to assess the relationship between high-fat dairy consumption and risk of obesity, CVD, and metabolic disease. 11 out of the 16 studies showed that high-fat dairy intake was inversely or negatively associated with measures of adiposity. In other words, those who consumed more high-fat dairy were less likely to be fatter. The researchers also found either no association or an inverse association between high-fat dairy consumption and metabolic diseases.
The results for the association between high-fat dairy intake and cardiovascular disease were inconsistent. However, this could be due to confounding variables not controlled for, as well as the differences in types of high-fat dairy products consumed in each study.
I think it’s also important to note that the observational studies used in this review were not able to separate dairy fat from other dairy components (such as casein, whey, and sugar), and were therefore not able to fully isolate the health effect of dairy fat. Further, the type of feeding practices, pasture-raised vs. grain-fed influences the composition of dairy fats and may negatively affect the results. In the future it would be interesting to conduct a study between individuals consuming organic and pasture-raised dairy compared to conventional dairy to see if any differences were observed in health outcomes.
Another study conducted a randomized control trial to compare the effects of the DASH (dietary approaches to stop hypertension, or high blood pressure) diet and a higher-fat DASH diet on blood pressure and lipid profile. The study was a crossover trial in which the 36 individuals in the study consumed a control diet, standard DASH diet, and high-fat, low-carb DASH diet for three weeks each, separated by 2 week periods. The modified DASH diet substituted low-fat dairy foods for full-fat dairy foods.
Overall, the researchers found that blood pressure was reduced similarly in the DASH and HF-DASH (HF= high fat, from dairy) diets compared to the control diet. However, the HF-DASH diet had better effects on lipid profiles than the regular DASH diet. The HF-DASH diet reduced triglycerides and VLDL. It also increased the particle size of LDL cholesterol compared to the normal DASH diet-- this means that the full-fat diet produced larger, more buoyant, non-sticky LDL cholesterol, without significantly increasing LDL levels!
This presents exciting evidence for a full-fat dairy diet for both reducing hypertension and risk of heart disease due to high triglyceride levels and small, dense LDL. A strength of this study is that the individuals had a high dietary compliance, which they measured through urine. It is also important that they conducted a crossover trial because this allowed for them to see the direct effects in each individual, instead of comparing one individual to another. However, the two week wash-out period was short to allow individuals to return to baseline and the 3 week intervention diet was also quite short to see long-term changes in blood lipid profiles and blood pressure.
According to an epidemiological study, the percentage of daily calories consumed from added sugars is almost 15%! This means that the average American eating a 2000 calorie diet is consuming at least 300 calories or 75 grams per day in added sugar! The study looked at the NHANES, a national survey that is representative of the US population, and adjusted for many factors such as age, sex, race/ethnicity, education, smoking status, physical activity level, and family history or CVD.
The researchers found that those who consumed 10-25% of their daily calories from added sugar were 1.3 times more likely to die from CVD compared with individuals who consumed less than 10% of their calories from added sugar. Those who consumed more than 25% of their daily calories from added sugar were almost 3 times as likely to die from CVD compared to individuals who consumed less than 10% of their calories from added sugar.
Even though these results are astounding, there are still some limitations to the study. First, some of the participants did not provide a second-day 24-hour dietary recall, so their usual diet may not be adequately represented. Also, for their analysis of the association, added sugar intake was only assessed at baseline and not updated during the follow-up period. It is possible that there were changes in added sugar intake over time. Despite the limitations of the study, this still presents important information for any added sugar consumption. Although most added sugar consumption in the US comes from sugar-sweetened beverages, this study prevents evidence that full-fat products may be better than low-fat, added sugar products.
In conclusion, it may not be the fat, especially the saturated fat, that is increasing risk for heart disease, but the added sugars! This is why it’s important to watch for labels and not be afraid of fat consumption, especially from pasture-raised, organic sources. I’d also like to mention that just because something is organic and grass-fed dairy doesn't mean that it is “healthy”. Take a look at the following products from the same company: the plain 2%, vanilla, and pumpkin pie-flavored Greek yogurt.
That’s all for tonight! Look out for my post next week discussing dairy and cancer.