Can antibiotics make you fat? - MOKOSH

Can antibiotics make you fat?

An interesting article in the latest issue of New Scientist (31 March 2012) entitled ‘Medicine that makes you fat’ – describes a study in which infant mice were fed low doses of penicillin for 30 days, to emulate the doses of antibiotics given to intensively reared farm animals in their feed. At the end of this time, mice fed the antibiotics were up to 15% bigger and twice as fat as mice on an antibiotic-free diet.

For decades, low doses of antibiotics have been routinely added to the food of intensively reared chickens, pigs and cattle to increase growth rates – this practice not only reduces the incidence of disease, it also makes the animals grow faster, requiring less feed and increasing profits for growers.

The mechanism by which feeding antibiotics results in weight gain in young growing animals is still not clear, but it seems that it is related to an alteration in the population of intestinal bacteria. This link was shown in a separate study where germ free mice were given either normal intestinal bacteria or intestinal bacteria from antibiotic-fed mice. The mice that received bacteria from antibiotic-fed mice were 35% larger than the other group after 5 weeks.

As humans are rarely exposed to long-term low doses of antibiotics, the next question is, do short-term courses of antibiotics, commonly used in humans, have an effect on our intestinal bacteria, and if so, do these changes increase the risk of weight gain?

A study carried out in Denmark followed 28,000 babies. Those given antibiotics within the first 6 months of life were more likely to be overweight at 7 years of age than those not given antibiotics, even if their mother was a healthy weight. This study suggests that even short term courses of antibiotics may cause long term changes in the gut bacteria of children, and may be one of the factors involved in the current increase in obesity in western countries.

It would be difficult to deny the huge benefits that humans and animals have received from the use of antibiotics, and it would clearly be negligent to forego the use of antibiotics for serious bacterial infections. However, in western society there are concerns that antibiotics are being over-prescribed, resulting in the development of antibiotic-resistant strains of bacteria. Feeding antibiotics to farm animals may also be contributing to antibiotic resistance. If it is true that the rise in obesity in society is also partly attributable to overuse of antibiotics, the cost to our health system of overuse of antibiotics is even higher.

It is worth noting that feeding of antibiotics is banned in organically raised animals – instead, management practices are aimed at reducing exposure to pathogens and other stressors, thereby reducing the requirement for antibiotic treatments. We believe these practices also improve the welfare of organically raised animals. Because the ‘crutch’ of antibiotics is forbidden in organic farming, animals cannot be raised in the stressful, high density environments of conventional intensive farms. In organic farming, good management, a natural diet and a low stress environment results in less disease, and therefore less need for antibiotic treatment.


At Mokosh, we believe that synthetic additives to both food and skin care, even in small quantities, may have long term deleterious effects on our bodies, even though to date there may be no proven negative effects of some of these compounds. When there is no need to expose ourselves to synthetic compounds, we should avoid them. We believe the best way to maintain long-term health is to base our diet on unprocessed plant foods, minimise consumption of animal products, and use only pure, unprocessed plant products on the skin. At the same time, choosing certified organic foods as much as possible not only limits our own exposure to synthetic compounds, but also reduces the negative impact of human agriculture on our ecosystem, and ensures a higher standard of welfare for farmed animals.

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