Global Harmonization of Methodological Approaches to Nutrient Intake Recommendations Proceedings of a Workshop (2018) / Chapter Skim
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6 Contextual Factors: Host, Diet/Environment, and Health Status
6 Contextual Factors: Host, Diet/Environment, and Health Status
Pages 83-116
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From page 83... ...
He showed evidence illustrating that although the strongest evidence for a diet-related gene remains for the lactase gene and its evolution to allow lactose tolerance, proof-of-concept evidence exists for several other diet-related genes. But the real question, he said, is whether genetic variation in diet-related genes matters in terms of nutrient requirements.
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From page 84... ...
for nutrient requirements, he said. Because baseline measurements of habitual intake, nutrient status, and body composition are so critically important, subjects need to be "normalized" before measuring these values.
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From page 85... ...
He listed four ways that infections can impair nutrient metabolism and, consequently, nutrient requirements: (1) decreased food intake, (2)
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From page 86... ...
Continuing the focus on bioavailability, Umi Fahmida discussed esti mates of bioavailability in Southeast Asian countries that were derived using the same tools described by Gibson. She commented on the variation in iron bioavailability data obtained from isotope studies for different types of diets across India, Myanmar, and Thailand (ranging from 2–20 percent)
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From page 87... ...
Food can also program the genome and change gene expression. Moreover, in humans, not only have dietary components throughout evolution contributed to today's genomes, but t oday's human genomes, in turn, code for food tolerances and intolerances, dietary requirements, and susceptibility to metabolic disease.
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From page 88... ...
. Stover found it interesting that selection for the calcium transporter gene occurred after selection for the lactose tolerance gene, that is, that the lactose tolerance gene allowed for consumption of milk first, followed by subsequent selection for a different gene involved in calcium transport.
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From page 89... ...
SOURCES: Presented by Patrick Stover, HMD Workshop, Rome, Italy, September 21, 2017 (Itan et al., 2010, modified with permission from BioMed Central)
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From page 90... ...
The question is: does this difference affect nutrient requirements? The answer is yes, he said, pointing to results of a 2008 study published in the Journal of Nutrition, where Solis et al.
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From page 91... ...
Stover explained how WHO broke the question down by deciding not to focus on either folic acid intake or neural tube defect risk, because of the errors associated with both of those measurements, but on the connection between the two: RBC folate concentration (see Figure 6-2)
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From page 92... ...
Based on this work, WHO (2015a) was able to recommend levels of RBC folate that are needed to prevent, or reduce the risk of, neural tube defects.
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From page 93... ...
, all of which need to be measured. "Normalizing" or Adapting Subjects Before Studying Nutrient Requirements Because of this physiological variation, Kurpad said, "I think it is extremely difficult to fulfill the requirements of a clinical drug RCT for nutrients." You cannot start a nutrient requirement RCT, he said, by "getting someone off the street" and giving them doses of the nutrient under consideration.
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From page 94... ...
"I think this is where we need to be clear," he said, and "harmonize all these different methods." The Problem of Scaling For Kurpad, in addition to the need to normalize, or adapt, subjects before studying nutrient requirements, scaling poses another challenge. He explained that requirements typically are scaled to body weight and not what he considers the "really important" components, like fat free mass.
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From page 95... ...
. Kurpad also emphasized the importance of functional endpoints when setting nutrient requirements.
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From page 96... ...
Decreased Food Intake Adu-Afarwuah described several studies showing that infectious diseases affect nutrient requirements by decreasing food intake, beginning with a study of children in Guatemala, ages 15–60 months, who either had or did not have selected common symptoms (Martorell et al., 1980)
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From page 97... ...
Again, Adu-Afarwuah described several studies from the literature demonstrating, in this case, that infectious diseases affect nutrient requirements by impairing nutrient absorption or reabsorption, beginning with a study of preschool children in Nigeria where the excretion of iron-labeled iron dextran, an indicator of protein loss, was higher in children with acute measles (Dossetor and Whittle, 1975)
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From page 98... ...
Thus, again, AduAfarwuah explained, both infection and the presence of fever cause excretion. In yet another study, 59 percent of preschool children hospitalized for shigella experienced urinary retinol loss, with 8 percent losing more than 0.1 micromole per day (Mitra et al., 1998)
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From page 99... ...
Moreover, in this case, after the infection has subsided, one's nutrient requirements would be even higher, as the infection would have depleted body nutrients stores to a large extent. Or, he continued to explain, if a person has a marginal intake before infection, then returning to the same marginal intake after the infection has subsided would mean a longer recovery period, during which time it would make sense to increase an individual's requirements.
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From page 100... ...
This reduced physical activity, in turn, leads to yet more muscle loss and becomes what she described as a "vicious cycle." Bone loss with age shows a similar trend, although some races are protected 4 This section summarizes information presented by Caryl Nowson, Ph.D., professor of nutrition and aging, Deakin University, Victoria, Australia.
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From page 101... ...
These findings raise the question: when making nutrient recommendations, how should this type of exercise, as well as other lifestyle factors, be taken into account? Other lifestyle factors that can affect nutrient requirements in the older population include smoking, which can have lifelong effects on bone density; high alcohol intake throughout life; industrialization, with the highest hip fracture rates in North Europe and the United States and the lowest in Latin America and Africa; and latitude, with a north–south gradient in fractures, which Nowson noted is perhaps related, to some degree, with vitamin D and cultural practices (i.e., covering up in the sun)
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From page 102... ...
But again, with respect to biochemical indices, serum calcium levels are of no use, Nowson remarked, and there are questions about the use of calcium balance studies given the unrealistic expectation that there will be no bone loss at 80 or 90 years of age, likewise, with physiological indices, such as bone density. She asked, "Do we really expect to have the bone density of a 30-year-old [at 80 or 90 years of age]
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From page 103... ...
Other nutrients can also affect calcium balance and, consequently, bone mineral density and structure. For example, insufficient protein can adversely affect calcium absorption, while a higher sodium diet can increase calcium excretion.
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From page 104... ...
, physical activity, skin cancer risk (people who have had skin cancer avoid sunlight) , food supply fortification, and dietary intake of calcium.
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From page 105... ...
According to Gibson, these include the following: 5 This section summarizes information presented by Rosalind Gibson, Ph.D., M.S.P.H., pro fessor emerita, Department of Human Nutrition, University of Otago, Dunedin, New Zealand.
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From page 106... ...
Methods Used to Estimate Bioavailability Several methods have been used in the past to estimate nutrient bioavailability: animal models; in vitro methods; in vivo methods, including isotopic methods; and changes in biomarkers or functional outcomes.
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From page 107... ...
m r The low bioavailability diet has an estimated 15 percent biovailability, a with a phytate:zinc ratio greater than 15 (cereal based with greater than 50 percent energy from unrefined cereals or legumes; negligible animal protein) ; the moderate bioavailability diet has an estimated 30 percent bioavailability, with a phytate:zinc ratio between 5 and 15 (not based on unrefined cereal grains or high-extraction rate [> 90 percent]
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From page 108... ...
As an example of data generated from the FAO food balance sheets, she referred to data from Wessells and Brown (2012) on mean daily per capita phytate:zinc ratios and fractional zinc absorption (as a percentage from the available food supply)
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From page 109... ...
• Explore the use of GIFT indicators for classifying diets as low, inter mediate, or high bioavailability for iron and zinc across countries. • Consider calculating dietary phytate:zinc molar ratios across coun tries using national food consumption survey data and the new phytate database; and exploring application of the Miller trivariate model for estimating fractional zinc absorption across countries.
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From page 110... ...
She noted the tools used to estimate bioavailability in the Asian region are the same as those described by Gibson, with isotopic studies being the "gold standard." As Gibson had, she also mentioned the FAO food balance sheets, which profile data from 210 countries; the WHO/FAO GEMS/Food cluster diet data from 183 countries; and National Food Consumption Survey (NFCS) intake data from the FAO/WHO GIFT platform, although not all countries are included in the GIFT platform, she noted, including Indonesia.
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From page 111... ...
This variation reflects the complexity of the diet in Asian countries, Fahmida remarked. Use of Food Balance Sheet Data to Estimate Bioavailability Food balance sheet data have been used to estimate energy obtained from animal source foods across Southeast Asian countries, expressed as both total kilocalories per day and percentage energy from animal source food.
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From page 112... ...
For zinc bioavailability, the committee deferred to the use of food balance sheet data to estimate fractional zinc absorption and also recom
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From page 113... ...
For zinc, while food balance sheet data allow for estimates of fractional absorbable zinc, in Fahmida's opinion, a better option would be to use NFCS data so bio vailability estimates are based on food intake, not food availability, a and will allow breakdown of bioavailability estimates by specific life-stage groups. Finally, for calcium, although calcium is a problem in Asian countries, Fahmida said, data are still insufficient to quantify the effects of absorption modifiers and, thus, bioavailability is not considered when setting calcium dietary requirements in Southeast Asian countries.
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From page 114... ...
Gibson emphasized the importance of using an evidence-based approach and the need to provide countries with advice on how to select studies in the literature from their own countries. For instance, many people are selecting studies with bioavailability data that are based on single meals, rather than on whole-day dietary intakes.
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From page 115... ...
Fahmida was not aware of any existing data from Southeast Asia on calcium balance, but repeated that calcium is considered a "problem" nutrient in the region with respect to intake level. Clifton remarked that it is only a problem compared to WHO suggested calcium levels, which he said, were Western based, not Asian based.
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