Editorial

See corresponding article on page 1498.

In this cohort, an apple a day could keep the doctor away1–3

Joanne R Lupton

A number of issues need resolution in terms of the potentialhealth benefits of dietary fiber, and the article by Buil-Cosialeset al. (1) in this issue of the Journal addresses most of them.Rather than being a study on total fiber intake and risk of onespecific disease, Buil-Cosiales et al. have addressed all-causemortality, parsed out the major causes of that mortality, andincluded intake of whole grains, fruit, and vegetables in theiranalyses in addition to total fiber. This study is a hybrid ofa randomized controlled trial (RCT)4 and an observational study,analyzed (appropriately) as an observational study. Being part ofthe parent 7447-person RCT provides important additional in-formation such as whether or not increasing fruit or fiber con-sumption over an ;6-y follow-up has an effect on all-causemortality. In addition, diet records were taken annually as partof the RCT, and Buil-Cosiales et al. used these repeated mea-surements of dietary information in their analyses, rather thanjust having one initial diet assessment at the beginning of a co-hort study, or just before and after values for intervention trials.Also of note is that the subjects in this study are elderly and allare at ‘‘high risk’’ of cardiovascular disease (CVD; having hy-pertension or type 2 diabetes or other risk factors) rather thanmost trials, which screen for only ‘‘healthy people.’’ Given thebreadth and novelty of this study, we now address what we cantake from it that will help advance our knowledge of fiber intakeand health.

IS THE FIBER PER SE PROTECTIVE, OR IS IT THEFOODS (e.g., WHOLE GRAINS, FRUIT, ANDVEGETABLES) CONTAINING THE FIBER THAT AREPROTECTIVE?

After a rather tortious debate over several decades, The In-stitute of Medicine of the National Academies (4, 5), CodexAlimentarius (2), and the U.S. Food and Drug Administration(3) have all addressed this issue and come to the same conclu-sion. If the fiber in fiber-containing foods is in a relatively intactform as found in the original plant, then it is considered ‘‘dietaryfiber.’’ Alternatively, if it is synthesized or extracted then putback into a food, there must be substantial scientific validationshowing a physiologic benefit to health before it can be countedas fiber. In laymen’s terms, this can be translated into ‘‘We’repretty sure that a fiber-rich diet is a healthy diet (so intact fiberfrom foods doesn’t have to prove itself), but we’re still unsure asto whether it’s the fiber in the foods or the fact that a plant-baseddiet high in whole grains, legumes, fruit, and vegetables isa healthy diet. That’s why if fiber is extracted from the plant it

does need to prove itself.’’ One way to shed some light on thisissue is to separate out fiber-containing foods from fiber per seand separately evaluate their associations with health outcomes,as was done in this article (1). Buil-Cosiales et al. evaluated theeffect of fiber and of different fiber-containing food groups onall-cause mortality. In theory, if the results showed that fiber wasmore strongly associated with lower all-cause mortality thanintake of any of the food sources of fiber, one might concludethat fiber per se rather than intake of the other fiber-containingfoods was the key driver of decreased mortality. Unfortunately,results of the study do not provide a clear answer to this ques-tion, but they are interesting nonetheless. With regard to baselinedata for the independent association of fiber, fruit, vegetable, andwhole-grain consumption with all-cause mortality: fiber intaketracked with fruit consumption and both showed a significantlylower total all-cause mortality (;37% risk reduction with fiberand ;42% risk reduction with fruit consumption). In contrast,neither vegetable intake nor intake of whole grains showed a sig-nificant trend toward decreased all-cause mortality. However, ifwe ask the question ‘‘Was the beneficial effect due to fiber intakeor intake of a particular food group?’’ (i.e., fruit), the answerisn’t clear, particularly because the major source of fiber in thisstudy was from fruit.

WHAT ARE THE SPECIFIC BENEFICIAL EFFECTS OREFFECT OF A HIGH-FIBER DIET?

Although the public and many scientists seem to consider thebeneficial effect of a high-fiber diet to be on the colon and coloncancer, the major clinical trials attempting to link intake of a par-ticular fiber, or increasing the amount of total fiber in the diet,have not shown a beneficial effect of fiber intervention on de-creased colon polyp reoccurrence after polyp removal (consid-ered the gold standard for a beneficial effect against coloncancer). Rather, when the Dietary Reference Intake (DRI) Com-mittee on the Macronutrients set intake values for dietary fiber,

1 From the Department of Nutrition and Food Science, Texas A&M Uni-

versity, College Station, TX.2 No financial support was received for this editorial.3 Address correspondence to JR Lupton, Texas A&M University, 123A

Cater Mattil, Mail Stop 2253, College Station, TX 77843-2253. E-mail:

jlupton@tamu.edu.4 Abbreviations used: CVD, cardiovascular disease; DRI, Dietary Refer-

ence Intake; RCT, randomized controlled trial.

First published online October 29, 2014; doi: 10.3945/ajcn.114.099960.

Am J Clin Nutr 2014;100:1409–10. Printed in USA. � 2014 American Society for Nutrition 1409

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the intakes were based on decreased risk of heart disease becausethis was where the strongest science was (5). The study by Buil-Cosiales et al. (1) is consistent with the DRI value for fiber beingbased on decreased risk of CVD (5), because they found a sig-nificant risk reduction for CVD with both high-fiber diets (54%risk reduction) and fruit consumption (56% reduction). Interest-ingly, more people in this cohort died of cancer (40% of the totaldeaths) rather than from CVD (24%), which is of particular notebecause the investigators purposely selected a population of in-dividuals with a high risk of heart disease.

DOES ONE HAVE TO HAVE A HEALTHY DIET FROMBIRTH OR CAN ONE ADOPT A HIGHER-FIBER DIETLATER IN LIFE AND GET SOME PROTECTION?

This is one of the most interesting findings from the study by Buil-Cosiales et al. (1). They divided the subjects into 1 of 4 categories:1) participants whose intake was low (lower fifth) in the baselinequestionnaire and who did not increase their intake (low/low), 2)participants whose intake was low in the baseline questionnaire andwho did increase their intake (low/high), 3) participants who wereadequate and remained adequate (high/high), and 4) participantswho were initially adequate but who decreased their intake (high/low). They found that if one was in group 2 (low at baseline butincreased fiber during the follow-up period), he/she had a lower riskof CVD than did the group who remained with a low intake (1).This is an interesting finding and could lead to other studies onswitching to a higher-fiber diet later in life.

ARE THE RESULTS TARGETED ONLY TO ‘‘HEALTHYPEOPLE’’ OR COULD PEOPLE WHO ALREADY HAVEHEART DISEASE BE PROTECTED BY EATING HIGHER-FIBER DIETS?

In most developed countries, dietary guidance, DRI values,and health claims are based on ‘‘healthy people,’’ which tendsto encourage investigators to use only healthy people in their tri-als so that their results can be considered toward establishingDRIs, dietary guidance, or health claims. This is probably oneof the most differentiating factors between the current study(1) and others, because the current study focuses on older in-dividuals who are at high risk of contracting CVD, not healthyindividuals. It is very clear from the study that these ‘‘at risk’’individuals still benefit from a diet that is not much higher thanthe lowest quintile in terms of fiber and fruit intake. And, if theyswitch from a low-fiber diet to a higher-fiber diet they willbenefit in terms of overall mortality.

DOES IT TAKE A MAJOR CHANGE IN DIET TO GETINTO THE PROTECTIVE CATEGORY FOR DECREASEDRISK OF ALL-CAUSE MORTALITY?

In the study described (1), the beneficial effect of fiber or fruiton all-cause mortality appears to have a threshold effect in thatthe biggest gain in benefit of intake of either fiber or fruit on

decreased risk of all-cause mortality is between the lowest quin-tile for fiber or fruit intake and the next quintile (quintile 2).Individuals who had a fiber intake of 17 g/d or 153 g fruit/d(quintile 1; called the reference on which the higher intakeswere evaluated) did not have a decreased risk of all-cause mor-tality, but just moving into the next highest intake level of fiberor fruit produced a benefit of ;37–39% decreased risk (seeTable 2 in reference 1). The difference in being in quintile1 and the beneficial quintile 2 for fiber is an extra 4 g (total of21 g). It is an additional 103 g for fruit. One medium apple(which is the most commonly eaten fruit in this cohort) contains182 g of fruit and has 4.4 g of fiber, which would mean thatadding 1 medium apple to the diet would put an individual fromthe lowest quintile (not protective) into quintile 2 (the protectivecategory) for both fruit and fiber.

In summary, this interesting article has shed light on a numberof issues that are currently being discussed in the fiber/health lit-erature and that need to be investigated in more detail. It showsthat certain food sources of fiber (in this case, fruit) may be asprotective against all-cause mortality as fiber itself, suggestingthat the food source of the fiber is important. It shows that themajor effect of a high-fiber diet is on decreased risk of all-causemortality, and the major contributor to that decrease in mortalityis decreased risk of CVD, which is what the DRI value for fiber isbased on. It also shows that it is never too late to switch toa higher-fiber diet, and even if one already has a predispositionto heart disease it still will be possible to decrease the risk byhaving a higher intake of fiber/fruit. Importantly, it would not takea major change in diet to go from no protection of quintile 1 ofintake to quintile 2 in which the beneficial effect is observed; theingestion of 1 medium apple would do this. All of these pointsrequire additional studies and verification, but they are indeedencouraging.

JRL is on the Mars Inc. Scientific Advisory Council but found no conflict

of interest between that position and this editorial.

REFERENCES1. Buil-Cosiales P, Zazpe I, Toledo E, Corella D, Salas-Salvado J,

Diez-Espino J, Ros E, Fernandez-Creuet Navajas J, Santos-LozanoJM, Aros F, et al. Fiber intake and all-cause mortality in the Prevencioncon Dieta Mediterranea (PREDIMED) study. Am J Clin Nutr 2014;100:1498–507.

2. Codex Alimentarius Commission. Report of the 30th session of theCodex Committee on Nutrition and Foods for Special Dietary Uses.In: ALLINORM 09/32/26 November 2008, paragraphs 27–54 and ap-pendix II, p. 46 (2009).

3. Department of Health and Human Services; Food and Drug Adminis-tration. 21 C.F.R. Part 101 Food labeling: revision of the Nutrition andSupplement Facts labels: proposed rule. Federal Register 79 (2014).

4. Institute of Medicine. Dietary Reference Intakes proposed definitionof dietary fiber. Washington (DC): The National Academies Press;2001.

5. Institute of Medicine. Dietary, functional, and total fiber. In: DietaryReference Intakes for energy, carbohydrate, fiber, fat, fatty acids, cho-lesterol, protein, and amino acids. Washington (DC): The NationalAcademies Press; 2002. p. 339–421.

1410 EDITORIAL

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