By Karl Nadolsky, DO, and Spencer Nadolsky, DO
Between high patient loads in the office, pharmaceutical reps pushing the latest and greatest drugs, and patients wanting a quick-fix, lifestyle-as-medicine can sometimes be overlooked. The Nadolsky brothers have taken on a mission to change that. This monthly column will review studies in the field and offer tips on how to incorporate new knowledge into practice.
This past month has delivered new information on two foods that always end up in the spotlight: nuts and meat.
One study supports our advocacy of including tree nuts, especially almonds, in a whole-foods dietary pattern. The other raises concern about red meat consumption — something we both enjoy and rely on for our muscle-building exercise regimens.
Before these papers came out, we had actually embarked on a month-long trial of eating strictly vegan to experience the most extreme plant-based type of diet there is. We’ll talk more about how that experience shaped our interpretation of these results and our dietary recommendations in general.
But first — let’s take a look at the studies.
Going Nuts
We have always been nuts about nuts, including them not only in our own diets but also in our dietary recommendations to patients.
This is due to the consistent cardiometabolic benefits suggested by the literature: improved glycemic control, reduced risk of coronary artery disease (recently the Physician’s Health Study and several meta-analyses), and reduced mortality.
The recent PREDIMED study included nuts as one of its interventions and showed that they lowered cardiovascular events. Greater frequency of nut consumption was also associated with lower mortality.
Much of the benefit has been thought to be due to their fatty acid profiles, fiber, lignans, and phytosterols with favorable lipoprotein effects.
Citing the plethora of data looking at almonds and lipids (one meta-analysis did, however, suggest a neutral effect on lipid changes from almond trials), Berryman and colleagues designed a very well controlled intervention comparing almonds with an isocalorically matched snack, while controlling for the rest of the diet.
They randomized 48 healthy patients to a crossover feeding trial with two 6-week periods, in which the diet was completely controlled (all meals were made by Penn State Metabolic Kitchens) and the only difference was the snack: either 1.5 ounces of unsalted whole almonds (about 250 calories per day) or a banana muffin with some butter (about 270 calories per day).
Both intervention groups had noteworthy improvements in lipids, but the almond intervention offered a significantly better improvement across the board.
Non-HDL cholesterol and apoB fell by 18mg/dL and 10mg/dL in the almond group, compared with 11 mg/dL and 5 mg/dL for the muffin intervention.
Ratios of total cholesterol:HDL-c, LDLc:HDL-c, and apoB:apoA1 were all also better in the almond group and statistically significant.
Remarkably, waist circumference actually decreased by nearly 2 cm in the almond group and by 1 cm in the muffin group. Although weight and body mass index (BMI) remained stable, this predicts a better cardiometabolic future.
The sample menu reveals that the overall quality of the prescribed diet was likely better than the average “SAD” (Sick American Diet), though certainly far from what I would recommend to any patient for cardiometabolic health, given that it included refined carbohydrates, fats, and juices (i.e., bagels, margarine, apple juice, dinner roll, etc.).
We feel this further solidifies evidence that clinicians should recommend almonds and other nuts when guiding patients in developing healthful dietary patterns.
Pumping Iron
Many popular dietary guidelines focus on limiting red meat for cardiovascular health due to its association with higher amounts of saturated fat and cholesterol. Some experts argue that since you can choose lean cuts of beef, the effects on cholesterol would be similar to eating other lean meat.
In fact there have been a few experiments done comparing lean beef to other lean sources of meat, both of which improved participants’ cholesterol and lipoproteins. Still, it has been found that red meat, especially from processed sources, is associated with cardiovascular disease and mortality.
This is disheartening (some pun intended) to folks like us who eat a few servings of red meat per week for both enjoyment and for protein to help us maintain and build muscle.
There have been multiple thoughts as to why this association with meat and heart disease still exists regardless of fatty acid and cholesterol content. One of the leading hypotheses is red meat’s high heme iron content.
The two sources of dietary iron are non-heme iron and heme iron. Non-heme iron is contained in both plants and animals, and is the type that Popeye promoted through his ingestion of canned spinach. Heme iron is contained exclusively in hemoglobin and myoglobin from animal sources and is absorbed much more readily than non-heme iron.
The thought is that heme iron may contribute to cardiovascular disease due to potential lipid peroxidation and other vascular effects from its high absorption rate, resulting in higher levels of body iron stores. Studies looking at actual body stores of iron using ferritin as a marker have been mixed in regards to cardiovascular disease.
To further investigate this hypothesis, Fang and colleagues conducted a meta-analysis that looked at the relationship of dietary iron and cardiovascular disease. This study was specifically looking for an effect of heme versus non-heme iron in regards to cardiovascular disease.
They included 13 prospective studies that evaluated exposures of dietary iron including heme, non-heme, and total iron. Each study used food frequency questionnaires to determine quintiles of dietary iron.
Indeed, Fang and colleagues found that heme iron — but not non-heme or total dietary iron — was associated with a higher risk of cardiovascular disease in a dose-response of 7% increased risk for each 1 mg/day increase in dietary heme iron. There was no trend for either non-heme or total iron intake.
The limitations of this study are similar to others like it, which includes the inability to prove causation. While there is biological plausibility, as explained above, there will likely never be a long enough randomized, controlled trial that would be able to show the effect we are looking for. This is why we rely on these epidemiological studies, for better or for worse.
Also, while red meat (beef in particular) tends to be the most demonized of all meats, do other types of meats contain high amounts of heme iron?
Indeed, looking at the USDA nutrient database, poultry and seafood/fish have somewhat similar heme iron content. Both beef and chicken liver have the highest amount.
Further research is being conducted looking at ferritin and potential benefits of lowering it, even in the normal range. It is possible that there is another compound other than the heme iron in meat that increases risk of cardiovascular disease. Researchers have been studying the compound trimethylamine-N-oxide (TMAO), which may be proatherogenic and increase in the serum via gut microbiota after eating L-carnitine containing foods such as beef.
This, however, would be contradictory to the positive secondary prevention of cardiovascular disease with supplemental L-carnitine.
As we completed this discussion, a very relevant review was published in “Meat Science,” which we would recommend reading, albeit understanding the inherent conflict of interest.
Takeaway
In the end, whether or not there is a specific compound in red meat that causes disease, it wouldn’t hurt to eat more plants and have an array of various lean protein sources other than red meat. We personally enjoy some beef two to three times per week in the form of 96% lean ground beef, sirloin steaks, N.Y. strips, filets, and occasionally rib-eyes. The fattier cuts of meat may have more biological plausibility for increasing risk of heart disease due to the postprandial lipemia.
So unless your patients are on a low-meat diet, consider sticking mostly to the leaner cuts of red meat just a few times per week.
Also, the question of grass-fed versus grain-fed often comes up. If you are choosing the leaner cuts of meat, we wouldn’t worry about it as the differences in fatty acid profile are small. Many will argue that it’s not about the health properties of grass-fed beef but more so the treatment of the cattle, but that discussion can be saved for another day.
Going back to the nut study, the key in advising patients is that nuts should be recommended in place of other snacks — especially refined starchy snacks.
While our vegan experiment was a worthwhile endeavor — and we absolutely acknowledge the data supporting a plant-based diet — we ultimately felt that there is a lot of confounding in the epidemiological studies of vegetarianism. At the same time, other epidemiological data and interventional studies have suggested benefits from fish, dairy, and other lean animal protein.