THE BLOG
01/14/2015 01:54 pm ET Updated Mar 16, 2015

Might the Fat Gene Make You Fat If You Were Born After 1942 and Received Penicillin as a Baby?

CamiloTorres via Getty Images

Born before 1942? If you were and also carry the gene for obesity, relax. The gene won't make you fat. Born after 1943? Yes, the gene might have a definite impact on your size. A study using information from The Framingham Heart study looked at the link between the FTO gene for obesity and actual weight. The Framingham Heart study is an ongoing research project, started in the middle of the last century to monitor the health of people living in and around Framingham, a town about 30 miles from Boston. The study has been going on for so long that the adult children of the original participants and their children are part of the study. Although many of the original participants have died, their records are available so their health status for example, their weight, can be compared with measurements made on their children and grandchildren.

Researchers at the Massachusetts General Hospital in Boston wanted to see if people with the FTO gene became obese; what they found was unexpected. According to James Rosenquist, lead author on the study published in the Proceedings of the National Academy of Sciences, it depended on birth year. Those with the fat gene born before 1942 did not become obese. Those born after 1942 were likely to be fat. This is true even among siblings from the same family born before and after 1942. For the almost-baby-boomers and beyond, there was a strong relationship between having the fat gene and being fat.

The reasons for the difference pre and post 1942? It's easy to find them. Packaged cake mixes, electric typewriters and then computers, TV remote controls, extension lines for the phone, drive-in services (so no walking is required to eat or bank), shopping malls, too much fast food, microwaves, clothes dryers, vending machines, super-sized portions, power lawn mowers and snow blowers, cheap food, automation, etc., etc., etc. The authors lump the reasons into one blame, and it's technology, which arguably does cover just about everything, excluding too large food portions, too little time to exercise, and inadequate sleep.

However, there is one factor that they did not mention, probably because the research is new and has been carried out on mice, but not people. That factor is penicillin, and its effect on the intestinal tract.

Our intestinal tract is inhabited by trillions of microbes, a fact few of us think about until we have a tummy ache. But there are scientists who believe that some of those trillions of microbes might affect whether or not we become fat. It is not clear how these microbes influence how much fat ends up in fat cells, or whether metabolism is speeded up or slowed down, but something seems to be going on. In a recent article in the December 25 issue of the New England Journal of Medicine, a rather startling discovery was reported. Scientists could make baby male mice quite fat simply by giving their mothers while pregnant and then nursing, low doses of penicillin. The antibiotic altered the intestinal microbes of the baby mice which in turn changed their metabolism and how their bodies responded to food. The mice became so obese as adults, they looked like mouse pillows with a head, a tail and a cushion-like body. The power of the penicillin-exposed microbes to turn skinny mice into candidates for Weight Watchers was confirmed when the microbes were given to germ-free mice and those mice gained fat and weight at a rapid rate.

So what does this have do with the fat gene and birth date? Probably nothing. But consider this. Something may have happened in 1940s to make it more likely that babies born with the fat gene would indeed become fat. And that was, for the first time ever, the easy availability of penicillin.

The military had access to penicillin during the Second World War but the rest of the country did not. Production of penicillin was limited until early 1944. In 1943, 21 billion units of the drug were produced in the United States. One year later, the number jumped to 1,663 billion units and then to more than 6.8 trillion units in 1945. Unlike the earlier years, distribution of the antibiotic was no longer restricted and everyone had access to it. Production continued to rise so by 1949, the annual production of penicillin in the U.S. was 133,229 billion units per year and it was now cheap.

So here we have one study that says something happened after 1942 to increase the likelihood of being fat if one has the obesity gene. We have another study, done with mice (so its relevance may be limited), that says changing the microbes in the gut with low doses of penicillin may cause obesity. And from 1944 on, penicillin rapidly became available to everyone.

Coincidence? It will take much more research to know. But it does turn research on obesity in a new direction. If the fat gene slows down metabolism for example, and if antibiotic altered microbes in our intestinal tract also slows metabolism (or increases the absorption of fat), it may explain why some people seem to gain weight so much more easily than others. Now if only researchers can discover how to alter our intestinal microbes so we can lose weight!