Is Dietary Fiber Associated with Reduced Mortality?

In an earlier I post I hypothesized that gut bacteria may be involved in mechanisms that affect lifespan. Because gut bacteria ferment dietary fiber to make short chain fatty acids such as butyrate, which may be involved in processes that mediate lifespan, investigation of large-scale epidemiological studies about the association between dietary fiber intake with all-cause mortality would be a good way to test this hypothesis. While this post won’t summarize all of the studies that relate fiber intake to mortality risk, in future posts I will sequentially investigate all the studies that have examined this association.

The Dietary National Institutes of Health-AARP Diet and Health Study (Park et al. 2011) included 567,169 men and women, aged 50–71 years who provided dietary intake data for a 9-year period. Dietary intakes were assessed with a self-administered 124 item food frequency questionnaire.

Compared with the lowest dietary fiber intake (13g in men, 11g in women), death from all causes was reduced by 22%, when compared with those with the highest intake (29g in men, 26g in women). So, the answer is to eat more fiber! I should say it’s easy to get 30 grams of fiber/day. That’s pretty close to my breakfast, which includes 100g of flaxseed, 35g yacon and ~90g of medjool dates.

Which dietary component was associated with this reduced risk, fiber from grains, fruits, vegetables or beans? Relative risk (including 95% confidence intervals) for men is shown in Table 1.

Grains Fiber Mortality Table 1

In comparison with the lowest grain fiber intake, those with the highest intake had significantly reduced risk of 23%, 23%, 17%, 52% and 26% death from all causes, cardiovascular disease, cancer, infectious diseases and, respiratory diseases, respectively. In women, fiber from grains significantly reduced mortality risk for each of these categories by 17-28%, with the exception of deaths from infectious disease. So, for the Paleo types who say don’t eat whole grains, the evidence doesn’t support that idea!

In Table 2 we see that fiber from fruits was not significantly associated with reduced mortality risk for any outcome. Does that mean don’t eat fruit? No. Fruit intake is well documented to be associated with improved health, so other components besides fruit fiber are likely involved.

Fruit Fiber Mortality Table 2

What about mortality risk for fiber from vegetables (Table 3)?

Vegetable Fiber Mortality Table 3

In men, compared with the lowest vegetable fiber intake, those with the highest vegetable fiber intake had 5% and 8% significantly reduced all-cause mortality risk and, cancer deaths, respectively. In women, all-cause mortality was significanty reduced by 5%, whereas respiratory disease deaths were reduced by 28%.

The association between fiber from beans with mortality risk is shown in Table 4.

Beans Fiber Mortality Table 4

Fiber from beans was not associated with reduced mortality risk for any outcome in men, but, all-cause, CVD, cancer and infectious disease deaths were significantly reduced by 13%, 17%, 3% and 41%, respectively in women.

The take home message? Eat more fiber!

If you’re interested, please have a look at my book!

References:

Park Y, Subar AF, Hollenbeck A, Schatzkin A. Dietary fiber intake and mortality in the NIH-AARP diet and health study. Arch Intern Med. 2011 Jun 27;171(12):1061-8.

 

Vegans, Vegetarians, Fish and Meat eaters: Which diet is best for minimizing risk of disease and death?

To answer the question proposed in the title, today I’ll look at the results of the Oxford Vegetarian study, in which risk for all-cause mortality, ischemic heart disease and malignant neoplasms was determined (Appelby et al.  1999). 6000 vegetarians and 5000 non-vegetarians were recruited, and, all participants were further divided into 4 groups: vegans, defined as those who never ate animal products; vegetarians, who never ate meat or fish but did eat dairy products, eggs, or both; fish eaters, who ate fish but no meat; and meat eaters (who ate meat more than once per week).

All groups consumed the same amount of total calories. However, when comparing individual macronutrients, vegans had the lowest protein (3.3% of total calories less than meat eaters) and fat intake (4.6 % less), but they made up for this difference by having a higher carbohydrate intake (9.5%), relative to all other groups. A similar dietary pattern was found in vegetarians, when compared with both fish and meat eaters.

A decreased total cholesterol/HDL ratio (TC/HDL) was found in vegans, when compared with vegetarians, fish and meat eaters  The TC/HDL ratio has been shown to be a strong independent predictor for the development of peripheral arterial disease (PAD, Ridker et al.  2001), a disease in which plaque builds up in the arteries that carry blood to the head, organs, and limbs. In vegans, TC/HDL = 2.88; in vegetarians, 3.25; fish eaters, 3.21; meat eaters 3.56. Based on these results, the incidence of ischemic heart disease was predicted to be 57% lower in lifelong vegans and 24% in lifelong vegetarians than in meat eaters.

When considered as a whole group (11,000 subjects), significant associations between individual dietary components and mortality risk for ischemic heart disease were determined. For example, eating up to 5 eggs per week did not significantly increase mortality risk, but eating 6+ eggs per week increased risk by 270%. Eating cheese (excluding cottage) up to 4 times per week did not increase mortality risk, but eating cheese more than 5 times per week increased mortality risk by 247%.  Relative to the lowest intake of animal and saturated fat, mortality risk was increased by 329% and 277%, in the highest intake, respectively. Similarly, those that ate the most cholesterol had a 353% increased mortality risk, relative to the lowest intake. In other words, high amounts of eggs cheese, animal and saturated fat were found to be associated with increased risk for ischemic heart disease.

Death rates, risk of ischemic heart disease and the risk of malignant cancer were 20%, 28% and 39% reduced in in non-meat-eaters when compared with meat eaters.Cumulatively, these results provide yet another reason to reduce meat consumption! (Also see http://michaellustgarten.com/2014/07/25/methionine-restriction-extends-lifespan-another-reason-to-reduce-meatprotein-intake/).

If you’re interested, please have a look at my book!

References:

Appleby PN, Thorogood M, Mann JI, Key TJ. The Oxford Vegetarian Study: an overview. Am J Clin Nutr. 1999 Sep;70(3 Suppl):525S-531S.

Ridker PM, Stampfer MJ, Rifai N. Novel risk factors for systemic atherosclerosis: a comparison of C-reactive protein, fibrinogen, homocysteine, lipoprotein(a), and standard cholesterol screening as predictors of peripheral arterial disease. JAMA. 2001 May 16;285(19):2481-5