December 2013 – When is sugar not a sugar?

We include ‘sugar’ in pig diets for many reasons such as palatability, energy and insulin manipulation. But particularly important is sugar’s role in keeping the beneficial bacteria in good order and therefore maintaining good gut health.

And it’s good gut health that drives feed intake. If the microflora of the gut is unbalanced, health and performance suffer as a consequence. So sugars in pig diets play important and varied roles. As nutritionists and producers, it’s interesting to understand a bit more about them and make sure we have the combination needed to do the job.

The primary use of sugar is to increase the sweetness of something. How ‘sweet’ our food is depends on our five taste senses: salty, bitter, sour, sweet and umami (savoury/meaty). Historically, increasing food ‘sweetness’ would indicate the energetic value of a feed, and the greater this value the more valuable that the raw material is in the diet, particularly in the wild when energy is in
short supply.

Post-weaning piglets would have their first sugar in the wild as fructose from fruit. This is a simple sugar – a monosaccharide – that, like glucose and galactose, is transported directly from the feed into the bloodstream.

Glucose is the primary fuel of the body, regulated by insulin production in the pancreas, and fructose and galactose are generally converted to glucose and other vital chemicals by various well-described pathways in the liver. These three sugars are vitally important and, in various combinations, make up the sugars we generally come into contact with.

For example, lactose is the sugar found in milk and is a combination of glucose and galactose. This is the very first sugar we would have been exposed to, and the enzyme lactase breaks down the lactose into its individual sugars.

Taking sucrose with a sweetness index point of 1.00 (a scale used by human food production to determine how ‘sweet’ something tastes), lactose comes in at 0.16. So lactose is of benefit to young mammals as an energy source rather than as a palatability agent as it doesn’t convey a great deal of sweetness to the finished feed. But it does have additional benefits in young animals as 10% of its consumption is used for prebiotic purposes, feeding the beneficial lactobacilli in the gut.

Sugars can be combined in such a way as to not be digested by the mammalian gut at all. Still looking at our ‘simple’ sugars, glucose and fructose can be put together to create fructooligosaccharides (FOS). These have a sweetness index of between 0.3 and 0.5, but don’t contribute any calorific value to a diet. They simply provide a substrate for microflora in the large intestine, improving overall gastrointestinal tract health. There’s also some evidence that FOS can increase calcium absorption, which would be an additional benefit.

All in all it’s a fascinating subject, and when someone next asks you to pass the sugar . . . ask them which type!

> Born in Essex, schooled in Suffolk and a graduate of Reading University, Dr Phil Baynes has spent his career in pig welfare and nutrition. Now based in Cheshire, he runs Baynes Nutrition and is a consultant nutritionist to Provimi

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