Feature: Why cats can’t taste sweet and how this helps pigs grow

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Ever wondered why it is best to give cats savoury foods or why piglets eat with such gusto? The answer lies in the gut and potentially the addition of a food additive commonly used to reduce calorie intake in human diets.

Artificial sweeteners are often used to replace sugar in some foods and drinks, but they are less known for their role in enhancing the health and well being of young animals.

In today’s intensive animal production, piglets are weaned at three or four weeks of age. This results in an increased number of piglets born per year.

However, weaning disorders such as diarrhoea, malnutrition and dehydration are one of most important problems in the animal production industry and result in 10% of premature pig deaths on farms. This is caused by immaturity of the gut structure and function and under-developed immune systems and gut microbiota.

At the University of Liverpool, Professor Soraya Shirazi-Beechey and her team at the Institute of Integrative Biology have been using several approaches including ‘metagenomic’ analysis to investigate how artificial sweeteners could be better used to help piglets build healthier guts and survive episodes of post-weaning intestinal disorders.

Using the state-of-the-art facilities at the Centre for Genomic Research, Professor Shirazi-Beechey’s team has identified the gut microbial population of piglets given a commercial diet and compared the changes in the gut microbial population of piglets given the same diet with added artificial sweeteners.

They discovered that inclusion of artificial sweeteners induced an increase in lactobacillus population in the gut.  Lactobacillus – a benign bacterium found in biotic yoghurts, and drunk by humans to improve the digestive system – secretes lactic acid which creates a hostile environment for harmful bacteria, cutting the incidence of diarrhoea. It also enhances the innate immunity by influencing the functioning of the gut immune system.

The work is funded by the animal feed company Pancosma SA, based in Switzerland  and is expanding to investigate the molecular mechanism by which artificial sweeteners increase the number of the beneficial bacterium.

“Pigs are weaned at approximately 28 days of age in the UK,” Professor Shirazi-Beechey explains.

“Once weaned they often struggle to adapt to a solid diet and because of the fall in nutrients, can have health problems.

She added: “Our work with Pancosma is about how we can benefit pigs and farmers without compromising on health and it’s a partnership that is driven by the research capabilities which are in place at Liverpool.”

How does your gut taste sweet?

Piglets also benefitted from another area of ongoing research in Professor Shirazi-Beechey’s laboratory.  Her laboratory was the first to show that the receptor that detects sweet tasting compounds in the tongue, is also expressed in enteroendocrine (sensor) cells of the intestine

She and her research team identified that this receptor, similar to that in the tongue, detects artificial sweeteners. Subsequently, they demonstrated that sensing of artificial sweeteners by this gut-receptor activates a pathway in the sensor cells of the gut. This results in secretion of a hormone called ‘glucagon like peptide-2’, which enhances gut structural maturity and intestinal glucose, salt and water absorption.

This discovery has led to the worldwide uptake of artificial sweeteners in the diet of early weaned piglets, improving the health and survival rates of piglets by preventing post-weaning intestinal disorders and creating significant economic benefits for the animal production industry.

Professor Shirazi-Beechey said: “Our work on sweeteners began with a discovery about their effect on cells lining the gut, but has since expanded to include work in genomics on the bacteria which live inside the intestine.”

The discovery of the gut sensor has implications for other animals as well.

Colic in horses is caused by a sudden intake of high grain diet with lots of starch so understanding the way the gut works and handles the food can be used to regulate their intake.

Fish farms are under pressure on environmental grounds to move from using food which is caught in the seas to plant-based nutrition, so understanding the way in which the fish digest and absorb nutrients can help with the correct formulation of their diet.

The work could also provide insight in the food preferred by domestic cats.  It is now known that cats do not have the ‘sweet’ sensor in their gut or in their mouths.  So while a sweet diet is good for livestock, cat food is very much best left in the savoury taste range!