Vegetables, Nuts and Overall Healthy Diet Protect Against Heart Disease

by | Apr 20, 2009
Vegetables

Vegetables

Most scientists agree that diet plays an important role in heart disease, but until now there has been no comprehensive analysis of which dietary factors most strongly affect disease outcome. A new meta-analysis published in the Archives of Internal Medicine reviews six decades of research (1950-2007) to assess how different dietary factors affect heart disease. Vegetables, nuts, “Mediterranean” and high-quality dietary patterns are strongly protective, while trans-fat, foods with high glycemic index or load and a “Western” dietary pattern were shown to be harmful.

The Study

This new study is unique for several reasons. First, the authors were only interested in factors that influenced heart disease directly, not simply heart disease risk factors such as cholesterol levels. Also, emphasis was placed on high-quality studies designed to identify strong dietary associations (cohort studies and randomized controlled trials) with long periods of follow up (at least one year). They asked whether the studies they reviewed were consistent with other data such as epidemiological reports, and sought to establish a causal link between diet and heart disease outcomes. Another important goal of the analysis was to identify factors that lack sufficient evidence to be conclusive and require further research.

Results

In addition to identifying vegetables, nuts, high-quality and Mediterranean dietary patterns as being strongly protective against heart disease, they also found monounsaturated fats (e.g. olive oil), dietary folate (e.g. whole grains, not supplements), dietary vitamins C and E (not supplements), alcohol consumption (in any form) and omega-3 fatty acids from fish (not plants, e.g. flax) to be moderately protective.

Factors that were not associated with heart disease in this study were dietary supplements (e.g. vitamins C and E), total fat, saturated fats, polyunsaturated fats (from plants), meat, eggs and milk. It is important to note, however, that negative findings in this analysis are not necessarily indicative of a lack of causality. Rather, it may indicate insufficient data to observe a significant positive association.

Dietary Patterns

The authors point out that “only overall healthy dietary patterns are significantly associated with coronary heart disease” in the controlled trials, while “evidence for most individual nutrients or foods is too modest to be conclusive.” They suggest that the reason an association exists for dietary patterns and not individual nutrients is that patterns “have the advantage of taking into account the complex interactions and cumulative effects of multiple nutrients within the entire diet.” The authors recommend future trials test various dietary patterns for disease outcome, including cardiovascular disease and cancer.

Taking this further, most dietary factors that were shown to be protective when consumed as part of a healthy diet were not protective when taken in supplement form. This finding bolsters the argument that overall diet rather than individual foods or nutrients are the best strategy for protecting against heart disease. The authors conclude that their findings suggest “investigating dietary patterns in cohort studies and randomized controlled trials for common and complex chronic diseases such as coronary heart disease.”

Based on their analysis, the dietary pattern that best protects against heart disease is rich in vegetables, nuts, fish, healthy fats, whole grains, and fruit. Likewise, the worst dietary pattern consists of refined carbohydrates and artificial trans-fats. The lesson: the best diet consists of plants, fish and whole foods, while processed foods contribute to heart disease.

What about red meat and saturated fats?

Interestingly, there was insufficient data to conclude that red meat or saturated fats are harmful for the heart. This is not terribly surprising, since the data has always been inconsistent. However, I would point out that many studies have looked at the role of red meat and saturated fat in coronary risk and the outcome always shows either harm or no result. And as explained above, no result can be indicative of a lack of statistical power rather than lack of causation. Importantly however, I cannot recall a single study suggesting that red meat and saturated fat is actually good for you.

From this the best we can conclude is that red meat or saturated fat may be involved in promoting heart disease, but if they are the effect is likely to be less harmful than a diet of processed foods. Practically this means small doses of saturated fat may not do much harm when eaten as a part of an overall healthy diet. This is a fairly compelling argument for exercising moderation.

Conclusions

Before you run out and order a ribeye, keep in mind that heart disease is not the only debilitating chronic disease that plagues our culture. Red meat is also associated with several kinds of cancer. Likewise, refined carbohydrates are highly correlated with type 2 diabetes. Vegetables and whole grains are protective against these other diseases as well, and fish may play a role in protecting against neurodegenerative diseases.

The take home lesson is that both diet and disease are complex systems that involve innumerable factors in several different regions of the body. When choosing what to eat it is important that you consider the context of your overall diet and do not get caught up is single foods or a single disease threat.

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12 Responses to “Vegetables, Nuts and Overall Healthy Diet Protect Against Heart Disease”

  1. Karin says:

    Great post! All these reminders about vegetables and fish have really impacted the way I think; I know I want to eat well, but still having difficulty taking the next step sometimes (sometimes I revert back to older eating habits….)- but I really do enjoy reading!

  2. Mike says:

    Whoa, I just caught something- you said that the omega-3s from fish are good, but the plant omega 3s are not protective?! Does that mean that I was conned into buying flax seeds and sprinkling them onto my foods, all for nothing?

    • Darya Pino says:

      Plant omega-3s may not be protective in heart disease, but that doesn’t mean they have no value. I’m sure there are many reasons flax is good for you.

      • Greg says:

        Like what? Is it better than any other grain or seed? Or are sunflower seeds just as good? Why would one source of omega-3s be beneficial, but a different source not have the same effects?

      • Darya Pino says:

        Omega-3s have different benefits because they are actually different chemicals. The same way different vitamins do different things.

        In this study, all nuts seem to have a major benefit for health, but we don’t really know why. Maybe it was the monounsaturated fats? Maybe it was the polyunsaturated fats that aren’t processed into pill form? All that matters is that we eat the nuts. Yum!

  3. Joe Alban says:

    Great post. Nice summery of a great study.

    I assume the study did not take into consideration the sources of the red meat. Do you know if there is information about the differences between grassfed organic red meat and CAFO? We localvoires love to tout that, but I am curious.

    • Darya Pino says:

      Great question!

      Michael Pollan discusses this a bit in the Ominvore’s Dilemma. Apparently red meat from grass fed cows (not sure organic matters – I would guess it is probably worse than grass fed because organic corn is still corn) has a better fat profile than corn fed cows: more omega-3s and fewer trans fats. I’m not sure how much of a difference this would make in the context of a whole diet with limited red meat (very small percentage of calories), but grass fed is certainly better for the environment and just about everything else in the world.

  4. Greg says:

    “only overall healthy dietary patterns are significantly associated with coronary heart disease”
    I love this. Basically tells people that are looking for shortcuts, to stop looking.

  5. Jean says:

    On red meat I think part of the reason for the mix results is the nature of commercial beef production. We started buying local protein about a year ago. And the local grass fed beef we bought was both *much* less fatty than beef bought in stores *and* had a much “meatier”, a much more dense, texture. We truly can’t go back and I’m certain that the effect of this beef on our bodies has different results than beef commercial raised and harvested.

  6. Kent Harris says:

    I’m just reading “Good Calories….” and find the grass fed vs grain fed bit misses the point. It’s the fat that makes us satisfied and ‘full’ longer. Of course we can overdo the quantity of anything i.e. I was told a choice 16 oz ribeye has the same amount of fat as a small can of Crisco shortening. Maybe a little disturbing, even disgusting put that way. My point is conversation about how lean meat is ‘better’ for us seems contrary to the evidence. Lean meat is less ‘filling’, meaning we will eat more of that huge baked potato and maybe a sweet after dinner drink too. Since there appears to be no credible evidence saturated fat causes heart attach or cancer, common sense would suggest when we replace the ‘satisfaction’ of eating fat with the satisfaction of eating refined carbs the effect is much worse. Don’t you agree?

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