Anyone reading the papers in the past few weeks could be forgiven for thinking that our nation has a deeply disturbed relationship with food.

On the one hand, we have Jamie Oliver’s admirable campaign to improve the muck dished up to our children at school. On the other, as London Fashion Week fills our pages with images of skinny boys and girls, we have politicians baying for them to be banned from modelling.

But while our attitude towards food might be troubled, one thing’s for sure — our appetite for it is still far too healthy. A recent government report warned that nearly a third of men in England will be obese by 2010 if current trends continue. Male obesity has practically doubled since 1993.

As our waistlines expand, so does the industry devoted to making us feel we’re trying to be healthy. Everything from eggs to ketchup is now available in an “organic” range.

But how can investors profit from all this? Certainly the big food companies that have taken on board the shift to healthy eating have been more successful in recent years.

The trouble is, food and fashion have a lot more in common than just eating disorders. Both are faddish. There may be a backlash against skinny models today but the mumsy look is highly unlikely to supplant heroin chic as the fashion industry’s default body shape of choice.

Similarly, although there may be a general trend towards healthier eating, it’s not always straightforward to pick out which companies will jump on the right bandwagons.

So what about the pharmaceuticals sector? One of the holy grails of drug manufacturers has been an anti-fat pill. The latest candidate in the frame is Sanofi-Aventis’s Acomplia, which helps dieters by making them feel full.

The good news is that Acomplia seems to avoid many of the problems that have plagued other diet drugs. However, it has yet to be approved for use in the US. And, of course, Acomplia is just one drug in Sanofi’s portfolio, so it is hardly the ideal way to get pure exposure — particularly as many of its other drugs will soon be coming under attack from rivals as patents expire.

The answer, as is often the case these days, is to look east. Not only are we outsourcing jobs to emerging markets, but we’re exporting our health problems too.

As developing markets become developed markets, the rise of the middle-classes — and their rising incomes and increasingly sedentary lifestyles — mean obesity may overtake communicable diseases as the main killer in India and China by 2020. And then, of course, there’s population growth.

This is one of the reasons that US investors such as Jim Rogers believe we are facing a long-term commodities boom, and that “softs”, or agricultural commodities such as grain, are particularly undervalued.

Some disagree, of course. In July, Ian Henderson, manager of the JPMF Natural Resources fund said: “There’s plenty of land that can be put to the plough if needs be.”

It sounds a rather compelling point. It certainly doesn’t take as long to bring a field into production as it might do to establish a new oil well, or construct a mine. But you don’t just need land to grow crops, you also need water. Lots of it.

Where will all this water come from? India’s water table is already plunging at a frightening rate, and hundreds of Chinese towns and cities are already facing water shortages.

Investing in water itself isn’t easy. You can’t trade it like a commodity, while utilities companies tend to be heavily regulated. But the good news is that trading in agricultural commodities is getting easier. Goldman Sachs offers two certificates — a type of tracker — linked to its agriculture and livestock indexes, you can spread bet on soft commodities, and ETF Securities (etfsecurities.com) is launching exchange-traded commodities that track the price of various agricultural commodities.

The commodities markets are volatile, but for the reasons outlined above, the long-term trend is for the cost of these goods to rise. After all — we may be faddish in our eating habits, but we still have to eat.

Merryn Somerset Webb is away

John Stepek is deputy editor of Money Week. His views are personal and investors should always seek professional advice

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