01.04.2016
Going Nuts Over Saturated Fats … Again
by Karl Nadolsky, DO, and Spencer Nadolsky, DO
Earlier, we exposed our learned favoritism of prescribing nuts as part of a healthy whole foods diet starting with a review of a RCT of almonds and lipoprotein levels. And we’vecontinued to discuss the nuances of recent evidence involving saturated fat and cardiovascular disease.
This month we again want to review some new evidence strongly supporting the inclusion of tree nuts in the diet for cardiometabolic health and also why liberal intake of saturated fat, generally speaking, may not be a great idea despite calls for stopping their demonization.
Nuts and Lipoproteins
Tree nuts have a reputation for improving cholesterol levels and have actually been studied extensively to see if they do that. Last month in the American Journal of Clinical Nutrition, Del Gobbo et al published a meta-analysis of 61 controlled intervention trials looking at a variety of tree nuts and their effects on lipoproteins and blood pressure. While there was no significant finding of blood pressure differences, improvements of atherogenic lipoproteins were consistent with expectations based upon previous analyses. The magnitude of just one serving of nuts daily (28 g) may not appear dramatic (5 mg/dL LDL-C and nearly 4 mg/dL apoB), but there was a dose response of a nonlinear fashion for LDL-C and a more dramatic effect on apoB in those with type 2 diabetes. Importantly, there was minimal heterogeneity amongst trials of different nut types.
The improvements in lipoproteins are thought to contribute to the reduction in cardiovascular events reported in observational studies of nuts. The calculated predicted risk reduction from the PREDIMED trial, however, does not match those studies. That is potentially due to other benefits such as glycemic control and endothelial function.
There was also another analysis of the PREDIMED trial, published last month, based upon an expanded prospective cohort that was followed until 2012. The analysis looked at intake of specific fat subtypes and CV events and death. The original PREDIMED trial showed decreased cardiovascular (CV) events in high risk subjects driven by significantly lower stroke rates over 4.8 years in those assigned to a Mediterranean diet supplemented with olive oil or nuts compared to control low fat diet. But for this study, subtypes of fat intake were broken into quintiles and events compared to the lowest quintile. After 6 years of follow-up, hazard ratios for those with the highest intake compared to lowest intake of total fat, monounsaturated fats, and polyunsaturated fats were 0.58, 0.5, and 0.68 respectively. The hazard ratios for highest intake of saturated fat and trans-fat were 1.81 and 1.67 respectively. Similar associations with risk of all-cause death were found and most remained after adjustment for several variables including BMI, smoking, other dietary factors, and other CV risk factors. When divided further, the culprit for saturated fatty acids (SFAs) was when the food source was pastries and other processed foods (cookies, donuts, bakery, pizza, sauces, etc). They also did analyses of isocaloric substitutions of dietary components for each other showing statistically lower CV events when replacing SFAs with monounsaturated fatty acids (MUFAs) or polyunsaturated fatty acids (PUFAs) and lower death replacing SFAs with PUFAs.
A few months ago, we reviewed a Cochrane analysis that looked at replacing saturated fat with foods containing mostly polyunsaturated fats. This substitution was associated with a reduction in mortality within randomized controlled trials. We noted that not all SFAs are created equally and we need to focus on the source or on whole foods.
We have discussed the health benefits of nuts numerous times now, but we haven’t discussed actually using this information in a clinical setting. From a practical standpoint, when prescribing nuts to your patients, a good starting place is ¼ cup, or about 30 g. This is usually the standard serving size and was also about the dose (28 g) used in the famous PREDIMED study. If the patient is trying to lose weight, have them get out their ¼ measuring cup since it is easy to overeat nuts when taking a big handful ().
We tend to favor raw nuts as opposed to salted roasted nuts when prescribing to patients, since the roasted type may be hyperpalatable and overeaten easily. On the other hand, if the patient doesn’t like raw nuts, roasted will work just fine since the nutritional value is very similar. Patients will just have to be mindful when eating them.
While PREDIMED involved almonds, walnuts, and hazelnuts, other nuts like cashews and pistachios hold health value too. In fact, peanuts, which are technically legumes, may have similar cardiovascular benefits and are much cheaper. If patients cannot afford mixed nuts, then peanuts may be a good alternative.
Conclusion
Our theme on this topic is the promotion of whole foods and avoidance of refined or highly processed foods, especially fatty foods. The body of evidence supporting the benefits of tree nuts is so strong that we should probably be suggesting most, if not all, patients should include them as snacks in their diet. More importantly, that advice can help replace the foods that are calorically dense and cardiometabolically adverse with these advantageous alternatives. And for the holiday season, which is “saturated” with a plethora of refined baked goods, we suggest that patients should instead consider sticking with roasting chestnuts over an open fire.
Karl Nadolsky, DO, is board-certified in endocrinology and in internal and obesity medicine.Spencer Nadolsky, DO, is a primary care physician board-certified in family and obesity medicine. Both have patient-facing blogs, at DocsWhoLift.com and DrSpencer.com.