Vegans studies

As an example, we will consider (Table 17.6) some changes that occurred in haemoglobin levels in a group of vegans when given vitamin B12 supplementation. The study was paired, each individual providing a pre-treatment blood sample and then a further sample after 4 weeks of supplementation. 

Zinc intakes of 6 Swedish vegans (individuals who consume no food of animal origin at all) using chemical analyses of diets from a duplicate portion sampling technique approach were included in a study by Abdulla et al. (12). Dietary fiber Intake of male subjects was 62+9 g/day and that of female subjects was 43 9 g/day. Zinc Intake of male subjects was 13 2.3 mg/day and that of female subjects was 6.5 1.3 mg/day, so as in the study of lacto-ovo-vegetarians by Anderson et al., subjects were found to have relatively high Intakes of fiber and relatively low Intakes of zinc with the zinc that was supplied being from foods believed to exhibit low zinc bioavailability. 

The use of food tables and nutrient databases to determine individual nutrient intake from food can be a major source of inaccuracy, as they may not contain comprehensive information on the nutritional content of all foods likely to be consumed by a study population. This is exacerbated in vegans who consume many unconventional foods not listed, or inconsistently listed, in such tables and databases. Moreover, micronutrients, which are found only in a small number of foods and in small quantities, are often poorly represented in nutrient databases. 

A number of investigations have studied the iodine intake of vegans (Table 45.3). The accuracy of the results from the five studies will ultimately depend on the dietary assessment employed. Two of these studies assessed iodine intake using the dupficate portion technique, while two estimated intake from food records, and the fifth study estimated iodine intake using a semi-quantitative food frequency questionnaire (FFQ). 

Two studies (Abdulla et al, 1981 Lightowler and Davies, 1998) used the duplicate portion technique to assess the iodine content of the vegans diets. Usual restraints and influences identified with this technique, such as the possible influence on dietary habits of collecting the food samples and gaining adequate cooperation from the subjects, might have been reduced in the Abdulla study that was undertaken in a controlled environment. These individuals consumed a modified diet to which they were unaccustomed, their iodine intakes would therefore not be a true reflection of their habitual diet. 

The findings from previous studies highlight the need to assess the iodine content of the vegan diet accurately. There are a number of factors that can influence the accurate assessment of iodine intake in vegans, including incomplete duplicate diet collections, the use of dietary supplements and the intake of dietary goitrogens. 

Previous studies assessing iodine intake in vegans have estimated intake from dietary supplements based on manufacturers declarations. Therefore, such intakes may be considered an approximation, as analysis has shown that the iodine content may differ from that stated on the packaging of the supplements and may also vary from tablet to tablet. 

Five studies have used biochemical markers to assess the iodine status of the vegan population (Tables 45.4 and 45.5). Three studies included measurements of thyroid function, while three measured the urinary iodine excretion of vegan subjects. 

A second study (Krajcovicova-Kudlackova et al, 2003) reported lower median urine levels among vegans as compared to lacto-ovo-vegetarians and omnivores (71 vs. 177 vs. 210 pg/day), but the ranges of the groups overlapped (9-204 vs. 44-273 vs. 76-423 pg/day) ... 

An English study (Lightowler and Davies, 1998), which had no control group, found that mean iodine content in vegan diets was 187 pg/day for women and 137 pg/ day for men ... 

A study performed in an iodine-deficient area of Sweden (Abdulla et al, 1981) found the vegan diet to be iodine-deficient, but did not consider the iodine content of an omnivore diet from that iodine-deficient region. 

Several studies found large inconsistencies between dietary iodine intake and urinary iodine excretion in vegetarians and vegans (Lightowler and Davies, 1998 Rauma et al., 1994, 1999). The most extreme example was a Finnish study of 9 vegans ( saxmzet al, 1994) mean dietary... 

These studies reflect the marked heterogeneity that can characterize vegetarian and vegan diets. In two studies, subjects were directed to avoid iodized salt, fish, seaweed and kelp, and iodine-containing processed foods, while only iodine-free beverages were provided (Abdulla et al, 1981 Remer et al., 1999). In these individuals, iodine... 

In addition to iodine measurements, three studies (Abdulla et al., 1981 Key et al., 1992 Raiuna et al., 1994) performed thyroid function tests as indirect measures of iodine sufficiency. Thyroid function was normal in two studies (Abdulla et al., 1981 Rauma et al., 1994). The third study reported elevated thyroid-stimulating hormone (TSH) levels in 5 of 48 vegans, but did not measure dietary or urinary iodine levels (Key et al., 1992). It is noteworthy that the three highest TSH levels were in vegans who usually took kelp it is possible that these three actually suffered iodine-induced hypothyroidism (Wiersinga and Braverman, 2003) secondary to the consumption of excessive iodine-rich kelp. 

Nutritional studies suggest that the iodine content of vegetarian diets may be inadequate, but adherence to a vegetarian diet need not lead to iodine deficiency. As diets become increasingly restrictive, assurance of adequate iodine intake increasingly depends on the appropriate use of iodized salt and other dietary supplements. Fortunately, the actual number of individuals who follow strictly vegan diets is small, and therefore so are public health risks of resulting iodine deficiency. 

As suggested several years ago by Herbert (1994), and confirmed by studies on vegetarian/vegan populations (Herrmann et al. 2003b), and more recently on elderly people (Valente et al. 2011), holoTC can be considered the very first marker of vitamin B12 deficiency (see Figure 28.2). 

Valuable information has come from a study of vitamin Bn deficiency in vegans, persons living on a purely vegetable diet without even milk or eggs (page 196). Other useful studies have come from regions of the world where animal foods are scarce or tabu, or where infestation with the fish tapeworm causes deficiency of the Autamin. 

Fecal characteristics like a low bulk, high pH and a high concentration of (secondary) bile acids observed in correlation studies, are also related to a high incidence of colonic cancer[4-7] For this reason we studied the effects on fecal bulk, defecation frequency, fecal pH and fecal bile acids of diets with different amounts and types of animal protein. The diets were chosen not only on account of differences in origin of protein, but also in order to provide customary diets containing meat, plant foods and milk-based products (lactovegetarian) or plant foods only (vegan). 

Vegetarian athletes have a limited choice of protein sources, especially if they are vegan. These athletes would almost require the inclusion of soy protein in their diet to be able to consume an adequate protein intake. While it appears that soy protein may not be the ideal choice for maximal muscle PS, it has been shown to be viable as a sole source of dietary protein. Studies have been conducted where soy protein was used to replace other protein sources without negative effects on the subjects. However, these tests were conducted in nonexercising individuals. As shown by Phillips, soy protein may not be the optimal choice for athletes and those seeking increased muscle mass. Additionally, because both resistance and cardiovascular exercise alone can decrease cardiovascular risks, " the benefits of including soy in the diet of an athlete may not be worth the potential decrease in attained muscle mass. However, sedentary persons may notice less of the diminished effect of soy protein intake than highly trained and competitive athletes. 

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