How does it work?
The digestive system is like a long, one-way tube, that takes in food (stomach), removes waste (feces), and in between extracts nutrients from food (the intestine – also called the gut, or bowel).
Initially, infants are only capable of processing a liquid diet, as they cannot yet break down solid food. Breastmilk provides complete source of nutrition in a simple, digestible liquid form that easily absorbed by the infant intestine. Milk formulas are designed to be like breastmilk in terms of nutritional composition.
As infants get older, their teeth and mouth enzymes are able to break down solids from 6 months of age. Their stomach fluids also become able to dissolve meat, cereals, fruit and vegies.
Further down, non-digested carbohydrates (dietary fibre) are digested by a population of billions of bacteria living in the gut called the microbiome. As a food ingredient, this is called “prebiotic” fibre, but in children, dietary fibre is just leftover plant carbohydrates that aren’t digested, and help form feces.
How does the digestive system absorb nutrients?
The intestine is where all nutrients from food are sent into the body. When food leaves the stomach, it is mostly a liquid form containing dissolved nutrients. About 15-30 minutes after feeding, these nutrients are slowly absorbed through the wall of the intestine, like tea through a tea bag.
The wall of the intestine is basically a folded up filter, with enough area to cover half a badminton court, so it is very good at absorbing!
Some nutrients like amino acids (from protein); simple carbohydrates (like glucose); water soluble vitamins (e.g. vitamin C, B-vitamins); electrolytes (e.g. calcium, magnesium) get across very easily. Others, like fats, DHA, EPA, ARA, vitamins A, D, E, and K, need extra help, because they don’t dissolve well.
When kids become ill through a gut infection, the intestinal wall becomes leaky and loses the ability to absorb. Also, bacteria and viruses can enter the gut, disturb the balance of gut bacteria, causing diarrhea and gas. They can even get into the body and cause infections in other places.
Digestive health, growth & development
Apart from zinc, a lack of any nutrient can impact on growth and development. The problem with trying to understand which nutrients are at fault is difficult because (a) that they work together, and (b) children with malnutrition may be missing most of the key vitamins and minerals. So complete nutrition is very important in preventing these problems.
- A double-blind, placebo-controlled, pilot study of bovine lactoferrin supplementation in bottle-fed infants – PubMed (nih.gov)