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Like many people, animals are getting fatter. At least, that is the finding of a report in the British publication, Proceedings of the Royal Society B. David Allison of the University of Alabama at Birmingham wrote the report.
Weight gain is often blamed on too much fatty food and too little exercise. But Professor Allison and his research team say there may be reasons other than these traditional ones.
The researchers studied body weight changes in more than 20,000 animals. The animals came from 24 populations of eight different species, or groups, across North America.
“Each animal was said to be in early middle age for its species. Yann Klimentidis worked on the study with David Allison. Mr. Klimentidis said they considered animals with at least two body weight measurements in the past 60 years. At least one measurement was made in the last half of the twentieth century. One exception was non-laboratory rats. Their body weight was first measured in 1948.
The study involved creatures as different as large animals in research centers and rats living free around Baltimore, Maryland. All the animals demonstrated major gains in average body weight over ten-year periods.
For example, chimpanzees in captivity showed a 33% increase in weight each decade. Laboratory marmosets increased weight at a rate of 9% over a ten-year period. Laboratory mice became fatter at a rate of 10%. And laboratory rats increased at a 3% rate.
The study also showed that pet animals are fatter. The average house cat weighed almost 10% more each decade. Dogs’ weight increased at a rate of 3%.”
A virus called AD36 could be involved in the gain. Its presence has been connected to obesity in adults. And the team says changes in time spent in light or dark environments influence eating habits.
David Allison says earlier studies found that light differences may be part of the reason for fatter animals. For example, one kind of animal – the lemming – experiences body weight changes at different times of the year.
“We know that light affects weight gain in species like lemmings that gain or lose a great deal of weight in different times of the year, when there is much sunlight versus little sunlight. That is the natural thing for them. So our brains are responsive to light and in ways that may relate to body weight.”
David Allison says changes in environmental temperature affect weight in both people and animals. The body produces more energy to keep itself warm in the cold. But it produces less energy to cool itself in heat.
“That all other things being equal, if you put a warm-blooded species like humans or mice or dogs into a colder environment, then they will need to expend more energy to maintain their body temperature. And so, being in a cold environment increases energy expenditure, and if you eat the exact same amount, will lead to lesser body weight. Being in a warmer environment, up to a point, will lead to decreased energy expenditure, and therefore, at the same amount of food intake, weight gain.”
Yann Klimentidis says knowing causes of weight gain in animals may help researchers as they deal with overweight human beings.