Feeding junk food to rats

Maternal “junk-food” feeding of rat dams alters food choices and development of the mesolimbic reward pathway in the offspring

Z.Y. Ong and B. S. Muhlhausler 2010

Background

Concerns about obesity in developed countries have led researchers to look at obesogenic lifestyles such as low physical activity and increased consumption of high fat/sugar food.

This research shows that if pregnant rats are fed junk food with high fat and sugar contents, both whilst pregnant and during lactation it changes the central reward system located in the brain known as the mesolimbic reward pathway. These changes lead to a higher preference for ‘palatable’ or high fat, high sugar foods.

The experiment

Twelve female Albino Wistar rats were individually housed and acclimatised to their environment for one week prior to commencement of the procedure. Control rats were given free access to standard rat chow while the JF (junk food) rats were fed a cafeteria junk food diet consisting of peanut butter, chocolate cookies, extruded savory snacks, processed meat and a mixture of lard and standard rat chow.

The rats were subjected to daily vaginal smears to determine the stage of their estrous cycle then mated.

After successful mating the females were returned to their individual housing and maintained on their respective diets throughout pregnancy and lactating.

After weaning, male and female pups were separated and all were provided access to both the standard rat chow and the cafeteria diet.

The dam and one female and one male pup from each litter were killed at weaning and a further male and female pup from each litter were killed at six weeks and three months of age for blood samples and tissue collection.

Results

On dissection of the rats it was found that the JF fed dams and pups had a high percentage of body fat, although this reverted back at three months of age.

The pups of JF fed dams showed a preference for fat from weaning to age three months

This study confirmed many previous studies of human and animal models (alluded to in the research paper) showing that increased maternal junk food intake affects food choice post weaning.

It was determined that this effect was caused by altered functioning of the central reward circuit leading to an increased penchant for high fat/sugar foods in a similar way to an addiction. Again this information was already in evidence, according to the authors.

There is a well-documented relationship between a mother’s high fat diet during pregnancy and lactation, and childhood obesity may be caused by alterations within the central reward pathway. What this work shows that hasn’t previously been illustrated is it can happen as early as three weeks after weaning. To clarify this concept the authors say that there will need to be four more studies.

The work was supported by the NHMRC.

Questions

What is the long term purpose of this study and how will it be applied to humans?

The author’s state that there is ‘Great opportunity in this field ...for interventions to block the early programming of an increased preference for fat/sugar...’ They state that this will be a means of controlling the obesity epidemic. The cornerstone to preventing obesity is major changes in food intake and exercise levels. Without changes to behaviour, a mother who eats junk food during pregnancy will continue in the same pattern throughout their child’s upbringing.

How will an overburdened health system with a small preventive care budget struggle to encourage mothers to abstain from junk food?

Why do we need more research confirming what has already been established in both human and animal-based studies? The study is repetitive and therefore a waste of resources.

Rats have a different metabolic rate, energy consumption and brain to humans. If more studies are required then pregnant humans with a body mass index over thirty would be more appropriate, and in fact much of the available research has already been conducted on humans.

What can you do?

Write to:
Associate Professor Pat Buckley
Sansom Institute for Health Research
GPO Box 2471, Adelaide SA 5001
IPC Address: CEA-06

Email: sansominstitute@unisa.edu.au

Animal Ethics Committee of the Institute of Medical and Veterinary Science
FOODplus Research Centre School of Agriculture, Food and Wine,
University of Adelaide,
Adelaide 5064

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