Alpha-amylase exists across taxonomic kingdoms with a deep evolutionary history of gene duplications that resulted in several α-amylase paralogs. Copy number variation (CNV) in the salivary α-amylase gene (AMY1) exists in many taxa, but among primates, humans appear to have higher average AMY1 copies than nonhuman primates. Additionally, AMY1 CNV in humans has been associated with starch content of diets, and one known function of α-amylase is its involvement in starch digestion. Thus high AMY1 CNV is considered to result from selection favoring more efficient starch digestion in the Homo lineage. Here, we present several lines of evidence that challenge the hypothesis that increased AMY1 CNV is an adaptation to starch consumption. We observe that α- amylase plays a very limited role in starch digestion, with additional steps required for starch digestion and glucose metabolism. Specifically, we note that α-amylase hydrolysis only produces a minute amount of free glucose with further enzymatic digestion and glucose absorption being rate-limiting steps for glucose availability. Indeed α-amylase is nonessential for starch digestion since sucrase-isomaltase and maltase-glucoamylase can hydrolyze whole starch granules while releasing glucose. While higher AMY1 CN and CNV among human populations may result from natural selection, existing evidence does not support starch digestion as the major selective force. We report that in humans α-amylase is expressed in several other tissues where it may have potential roles of evolutionary significance.

Background Over the past several decades, rural and indigenous populations in Latin America have experienced abrupt and profound transformations in their lifestyles and economies, many having remarkable health consequences. Yet, these changes have had heterogeneous effects on the population's biology in different local contexts. Objectives The primary goal was to characterize the nutrition transition and biomarkers of noncommunicable diseases (NCD) risk in 2 Chilean indigenous populations that have had divergent histories of subsistence strategies (agropastoralism compared with hunter-gathering) in the last few millennia and live in contrasting environments, and to identify context-specific factors driving the nutrition and epidemiological transitions. Methods One-hundred-and-ninety (90 Pehuenche and 100 Atacameño) participants aged 18–87 y completed demographic, food-frequency, and physical activity questionnaires as well as measurements of some NCD risk biomarkers: blood pressure, weight, height, body fat percentage, waist circumference, blood total cholesterol, HDL cholesterol, triglycerides, and glucose. Framingham risk scores (FRSs) were calculated based on age, sex, total cholesterol, HDL cholesterol, systolic blood pressure, smoking, diabetes status, and hypertension medication. Results Few differences in dietary composition and physical activity patterns were observed between the 2 populations. Multivariate analyses showed no differences between the 2 populations in any of the individual NCD risk biomarkers or FRSs after adjusting for age, sex, time since last meal, food insecurity in childhood, ultraprocessed food consumption, and physical activity. Conclusions Despite contrasting ecological and historical contexts, the 2 groups are converging into similar processes of market and wage-labor integration and transitioning to a Western diet high in processed and nonlocal foods, although some aspects of their “traditional” foodways are still in practice. The frequency of individuals exhibiting NCD biomarkers “at-risk” is relatively high and corresponds to other populations that have gone through nutrition transition. Furthermore, none of these biomarkers or FRSs differed between the 2 populations, suggesting a homogenization in the NCD risk factors.

Although the frequency of LP varies among the populations according to their degree of admixture, dairy consumption was very low across the populations. Given that the association between milk consumption and expected phenotype was found only in two of the populations analyzed, it seems that lactase non-persistence (LNP) is not the only cause for dairy avoidance. Thus, it is suggested that SES and cultural preferences are likely affecting dairy consumption.

Lactase persistence (LP) occurs at a very low frequency in indigenous populations from Latin America, offering an opportunity to understand the relationship between this genetic trait and patterns of dairy consumption. Here, the frequency of LP is analyzed from Mapuche and -an adjacent- mestizo population inhabiting the Araucanía region. In addition to genotyping for LP, participants were surveyed in relation to general perception and consumption habits of dairy products. Low LP frequency (10%) and very low dairy intake was found among the Mapuche population as compared with Mestizo populations inhabiting Chile. The survey reported that the main reasons for avoidance of dairy were the gastrointestinal symptoms after dairy intake and cultural dietary habits. The interaction between low LP genotype frequency, low dairy intake, and sociocultural determinants is here discussed in the light of their potential health outcomes.

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