Through cultural innovation, and changes in available food types with the changing habitat and there have been a number of major dietary shifts in human evolution, including meat-eating, cooking, and those associated with plant and animal domestication. The identification of signatures of adaptations to such dietary changes in the human genome sheds light on the evolutionary history of our species’ metabolism.

Once upon a time, sugar was sold as a spice, it was used as a medicine, and it was a luxury food only the rich could afford. However, by the 19th-century sugar became a staple of the working-class diet, and often used as a food preservative such as in jam.

What we casually refer to as [table] sugar in our everyday lives is sucrose sugar, and there are several other types of sugars.

Type of SugarSource of Sugar
SucroseSugar cane, sugar beet
GlucoseHoney, corn syrup
FructoseMost fruits
LactoseMilk and milk products
Basic Sugars

Because the human body can produce energy only from the glucose sugar digestion system of the body must break other types of sugar, including lactose sugar, down to glucose sugar before they are observed into the bloodstream. Types of sugars that the body cannot break down to glucose sugar end up in the large intestine for excretion.

Various types of sugars for human consumption.
Various types of sugars for human consumption.

Lactose Sugar

It is the lactase enzyme that helps the human body break lactose sugar down to glucose. This enzyme is produced in high quantities at birth in order to break down the lactose sugar in the mothers’ milk. However, as the infant grows reliance on the mother’s milk lessens and eventually finishes. In correlation with this, in most cases, the small intestine produces little to no lactase enzyme. As a result, lactose-tolerant born babies usually grow up and become lactose intolerant adults.

Since lactose intolerant adults lose the ability to digest the lactose sugar in their intestines partially or totally, undigested sugar is passed on to their large intestines where it gets broken down by bacteria, which causes gas, bloating, stomach cramps, and diarrhea.

Lactose Intolerance Worldwide Distribution Map

Worldwide most people are lactose intolerant, however, because lactose intolerance is genetic the distribution of people with this digestive disorder or there lack of is not homogenous. For instance, in Ireland and Great Britain almost all adults, in the rest of Europe most adults can have milk and milk products in their diets with no problems but in areas where ethnic Europeans are the minority, on the other hand, either most or almost everybody is lactose intolerant.

Early Europeans

First modern humans that immigrated to Europe were mostly lactose intolerant too. However, in Europe, the ability to digest milk and milk products of domesticated animals is thought to be a favorable trait that created a bottleneck. In other words, lactose intolerance was such a disadvantage that individuals without this digestive disorder were more likely to survive long enough to pass on their genes to their offspring.

Most scientists believe lactose tolerance was critical in Europe because:

  • Sun exposure was relatively less in Europe and people were in greater need of vitamin D found in cow’s milk.
  • Cow’s milk provided a much safer and cleaner alternative to drinking water that may cause disease.
  • Those who could not tolerate lactose would die of starvation, while those who could tolerate lactose would survive.

Conclusion

In conclusion, in the past lactose intolerant Europeans were more likely to die of starvation, Vitamin D deficiency, or drinking contaminated water before having children compared to those who could digest milk and milk products past their infancy such that today 70% of ethnic Europeans are lactose tolerant while for the rest of the ethnic groups “lactose tolerance” remains an anomaly.

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