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Vegetarian Nutrition

VN: Types and Diversity of Vegetarian Diets (2009)

Citation:

Sabate J. The contribution of vegetarian diets to health and disease: A paradigm shift? Am J Clin Nutr. 2003; 78 (suppl): 502S-507S.

PubMed ID: 15806870
 
Study Design:
Narrative Review
Class:
M - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

Sabate draws on several decades of research to develop three models depicting the population health risks and benefits of vegetarian and meat-based diets. This series of models encapsulates the evolution of scientific understanding on the overall effects of these dietary patterns on human health.

Note: This article provides a theoretical framework to understand the findings of a systematic review. The methods described are, therefore, the methods for the systematic review.

Inclusion Criteria:

Not specified in this article.

Description of methods for systematic review described in: Sabate J, Duk A, Lee CL. Publication trends of vegetarian nutrition articles in biomedical literature, 1966-1995. Am J Clin Nutr. 1999 Sep;70 (3 Suppl): 601S-607S.

  • Articles in the MEDLINE database
  • The years included in the analysis were 1966 when MEDLINE was initiated, through 1995 the last year for which complete information was available at the time of the search
  • Records were used that satisfied the following criteria: Any record indexed by MEDLINE; any record that contained the key term vegetarianism, vegetarian, or vegetarians; any record in a journal that was indexed by MEDLINE as a nutrition journal; or any record that contained the vegetarian key terms and was found in a nutrition journal
  • Additionally, a journal in which an identified article was published was then searched
  • The search was done only in even-numbered years from 1966 to 1995.
Exclusion Criteria:
  • Article not available in bound form at the Loma Linda University library
  • MEDLINE records did not contain sufficient information
  • The article dealt with entomology, zoology or anthropology
  • The studies were in animals and had no direct application to human diets
  • Mention of the word vegetarian was coincidental.
Description of Study Protocol:
  • Design: Narrative review (theory) based on systematic review.
  • Statistical analysis: Chi square.
Data Collection Summary:
  • Timing of measurements: Articles published between 1966 and 1995
  • Dependent variables: Nature of research on vegetarianism
  • Independent variables: Cultural views of vegetarianism and research methodology.
Description of Actual Data Sample:
  • Initial number of articles identified: 1309
  • Final number of articles used in systematic analysis: 587.
Summary of Results:

Sabate reviews the research on vegetarian diets over the past several decades and argues that there has been a paradigm shift in the way researchers have come to think about and examine vegetarian diets.

Three Models

Up to the 1970's: Is a Vegetarian Diet Safe?

According to Sabate, early research (up to the 1970's) focused on the nutritional adequacy of vegetarian diets. That is, the concern was whether it was possible to adhere to a vegetarian diet and still obtain the minimal nutrients and energy necessary for human growth and reproduction. Sabate notes that the focus of research on vegetarian diets during this period was largely based on case studies of nutrient deficiencies and adherents to vegetarian diets were often viewed as counter-cultural or vegetarian for reasons other than health (e.g., religion).

With the greater affluence of industrialized countries came the realization that many chronic and degenerative diseases had a dietary component and that all diets have both potential risks as well as benefits. While there were risks, nutrient adequacy was (and is) still an issue in impoverished settings (e.g., in some developing countries), research began to find that it was not the plant-based diet per se that was the cause of nutritional deficiency, but more a function of how restrictive the diet was. For instance, some plant-based diets were highly restrictive because of lack of access to a range of foods (e.g., in a poverty setting) or because of choice (e.g., macrobiotic diets). Sabate notes that it is in these situations of food restriction that nutritional deficiencies were more common.

However, as research broadened to focus on plant-based diets that were well planned and not highly restrictive, findings began to appear suggesting that not only could a plant-based diet be adequate, but it could have concrete health benefits.

Sabate carries out a systematic review of vegetarian research articles published between 1966 and 1995 and finds that the focus of research shifts away from issues of nutritional adequacy to issues of the preventative or therapeutic benefits of vegetarian diets. Sabate demonstrates this by presenting the relative proportion of vegetarian nutrition articles published on the different themes during the successive time periods. (Table 1)

1980s and 1990s: From Deficiencies to Benefits

Sabate notes that over the past 20 years, there has been a shift in the research focus on vegetarian diets. Larger epidemiological studies of vegetarian populations (especially those of the Adventist Health Study) began to demonstrate the health benefits of plant-based diets. Sabate provides a table that summarizes the findings from this series of studies.

What is significant about these studies is not simply the findings that meat may be associated with certain types of cancer and heart disease, but that some foods common to plant-based diets can have a protective effect against these diseases.

 

Protective (Reduces risk)

Hazardous (Increases risk)

Cancer site

Colon

Legumes

Meat

Lung

Fruit

No relation

Pancreas

Legumes, Plant protein products, Dried fruit

No relation

Bladder

No relation

Meat

Prostate

Legumes, Tomatoes, Soy milk

Meat

Breast

No relation

No relation

Ischemic heart disease

Myocardial infarction

Nuts, Whole-grain bread

No relation

Fatal ischemic heart disease

Nuts

Meat

Studies Cited:

Fraser GE, Beeson WL, Phillips RL. Diet and lung cancer in California Seventh-day Adventists. Am J Epidemiol 1991; 133: 683–693.

Fraser GE, Sabate J, Beeson WL, Strahan TM. A possible protective effect of nut consumption on risk of coronary heart disease: The Adventist Health Study. Arch Intern Med 1992; 152: 1,416–1,424.

Jacobsen BK, Knutsen SF, Fraser GE. Does high soy milk intake reduce prostate cancer incidence? The Adventist Health Study. Cancer Causes Control 1998; 9: 553–557.

Mills PK, Beeson WL, Abbey DE, Fraser GE, Phillips RL. Dietary habits and past medical history as related to fatal pancreas cancer risk among Adventists. Cancer 1988; 61: 2,578–2,585.

Mills PK, Beeson WL, Phillips RL, Fraser GE. Bladder cancer in a low-risk population: results from the Adventists Health Study. Am J Epidemiol 1991; 133: 230–239.

Mills PK, Beeson WL, Phillips RL, Fraser GE. Cohort study of diet, lifestyle, and prostate cancer in Adventist men. Cancer 1989; 64: 598–604.

Mills PK, Beeson WL, Phillips RL, Fraser GE. Dietary habits and breast cancer incidence among Seventh-day Adventists. Cancer 1989; 64: 582–590.

Singh PN, Fraser GE. Dietary risk factors for colon cancer in a low risk population. Am J Epidemiol 1998; 143: 761–774.

Snowdon DA, Phillips RL, Choi W. Diet, obesity and risk of fatal prostate cancer. Am J Epidemiol 1984; 120: 244–250. 

Current Research: From "Beneficial" to "Optimal"

But, might a plant-based diet be more than simply “safe” or even “beneficial”? Could a plant-based diet be optimal? Sabate says yes.

Sabate uses a risk-to-benefit ratio estimation to argue for the advantages of a plant-based diet over a meat-based diet.

First, Sabate argues that exchanging a small amount of vegetables in a plant-based diet for dairy products or eggs would have substantial benefit by decreasing the risk of nutritional deficiencies but only a minimal increase in the risk of coronary diseases. In contrast, Sabate says that it would take a major change in a meat-based diet to bring about benefits and decrease risks. In short, only a small modification to a plant-based diet is needed to avoid risks and increase benefits, while a major change in a meat-based diet is needed to bring the same benefits and decrease risks.

Second, Sabate suggests that the increased risk for cancers and cardiovascular diseases may be a result not merely of excesses of energy, total fat, etc., but may actually be caused by a deficiency in phytochemicals and other compounds found in plant foods. The problem, as Sabate sees it, is that we do not yet have enough knowledge about these plant-based compounds to be able to define what a “deficiency” in these compounds means.

The bottom line, as Sabate sees it, is that chronic and degenerative diseases may not be brought about merely by excesses of particular foods or nutrients, but may be brought about by deficiencies in certain important plant-based compounds.

The Bottom Line

Sabate argues that the paradigm for understanding vegetarian diets has changed over time. This progression can be represented as a succession of questions that have motivated nutritional research on vegetarianism:

  • Is a vegetarian diet nutritionally adequate?
  • Are there benefits to a vegetarian diet?
  • Might a vegetarian diet actually be optimal?

In Sabate’s interpretation of the research, a plant-based is not merely adequate, but it may in fact, be optimal.

Author Conclusion:

In conclusion, recent scientific advances seem to have resulted in a paradigm shift. Diets largely based on plant foods, such as well-balanced vegetarian diets are viewed more as improving health than as causing disease, in contrast with meat-based diets.

Funding Source:
University/Hospital: Loma Linda University
Reviewer Comments:
Excellent piece of overview or theoretical perspective based on systematic review.
Quality Criteria Checklist: Review Articles
Relevance Questions
  1. Will the answer if true, have a direct bearing on the health of patients? Yes
  1. Will the answer if true, have a direct bearing on the health of patients? Yes
  2. Is the outcome or topic something that patients/clients/population groups would care about? Yes
  2. Is the outcome or topic something that patients/clients/population groups would care about? Yes
  3. Is the problem addressed in the review one that is relevant to dietetics practice? Yes
  3. Is the problem addressed in the review one that is relevant to dietetics practice? Yes
  4. Will the information, if true, require a change in practice? Yes
  4. Will the information, if true, require a change in practice? Yes
 
Validity Questions
  1. Was the question for the review clearly focused and appropriate? Yes
  1. Was the question for the review clearly focused and appropriate? Yes
  2. Was the search strategy used to locate relevant studies comprehensive? Were the databases searched and the search termsused described? Yes
  2. Was the search strategy used to locate relevant studies comprehensive? Were the databases searched and the search termsused described? Yes
  3. Were explicit methods used to select studies to include in the review? Were inclusion/exclusion criteria specified andappropriate? Wereselectionmethods unbiased? Yes
  3. Were explicit methods used to select studies to include in the review? Were inclusion/exclusion criteria specified andappropriate? Wereselectionmethods unbiased? Yes
  4. Was there an appraisal of the quality and validity of studies included in the review? Were appraisal methodsspecified,appropriate, andreproducible? No
  4. Was there an appraisal of the quality and validity of studies included in the review? Were appraisal methodsspecified,appropriate, andreproducible? No
  5. Were specific treatments/interventions/exposures described? Were treatments similar enough to be combined? Yes
  5. Were specific treatments/interventions/exposures described? Were treatments similar enough to be combined? Yes
  6. Was the outcome of interest clearly indicated? Were other potential harms and benefits considered? Yes
  6. Was the outcome of interest clearly indicated? Were other potential harms and benefits considered? Yes
  7. Were processes for data abstraction, synthesis, and analysis described? Were they applied consistently acrossstudies and groups? Was thereappropriate use of qualitative and/or quantitative synthesis? Was variation in findings among studies analyzed? Were heterogeneity issued considered? If data from studies were aggregated for meta-analysis, was the procedure described? Yes
  7. Were processes for data abstraction, synthesis, and analysis described? Were they applied consistently acrossstudies and groups? Was thereappropriate use of qualitative and/or quantitative synthesis? Was variation in findings among studies analyzed? Were heterogeneity issued considered? If data from studies were aggregated for meta-analysis, was the procedure described? Yes
  8. Are the results clearly presented in narrative and/or quantitative terms? If summary statistics are used, are levels ofsignificance and/or confidence intervals included? Yes
  8. Are the results clearly presented in narrative and/or quantitative terms? If summary statistics are used, are levels ofsignificance and/or confidence intervals included? Yes
  9. Are conclusions supported by results with biases and limitations taken into consideration? Are limitations ofthe review identified anddiscussed? No
  9. Are conclusions supported by results with biases and limitations taken into consideration? Are limitations ofthe review identified anddiscussed? No
  10. Was bias due to the review's funding or sponsorship unlikely? Yes
  10. Was bias due to the review's funding or sponsorship unlikely? Yes