When we were growing up in the 1980s and 1990s, the only person I knew who used to grow jatropha trees was my great grandmother. In those days, we called them mifareki.

The brown seeds the trees produced were a delicacy for pigeons but occasionally my great grandmother would pound them and coax us to swallow a little of the oil to still our stomach pains.

Now, jatropha trees have become the next big thing in agribusiness and many NGOs have sprouted in rural areas encouraging farmers to grow the crop to produce biofuels as one way of countering the rising fuel prices.

One such organisation, Global Development of Peaceful Environments, is working with General Motors in Kenya to grow jatropha trees whose oil is used as fuel for some of the company's motor vehicles, including matatus.

The argument used by those who support the use of these plant-based fuels has been that such fuels are friendly to the environment.

However, a new crop of thinkers is questioning this claim. They are also raising concerns that fuel from plants is partly to blame for rising food prices.

Michael Grunwald, in an article published by Time magazine, noted that large tracts of forests and wetlands are being destroyed across the world to create room for land on which to plant fuel crops.

In countries such as the US, maize is increasingly being converted from a food crop to a fuel crop.

According to Grunwald, the amount of maize used to fill the petrol tank of a Hummer can feed one person for one year.

This means that the more we use maize to fuel Hummers, the more people go hungry because we are giving to cars what we should be giving to hungry people.

In Kenya, many farmers are turning their backs to food crops like maize because they have discovered that growing crops like jatropha on a large scale makes better business sense.

The jatropha seeds are fetching attractive prices because the demand is high. The worry is that once this business is adopted on a large scale, hardly anyone will be growing maize any more, and the country is likely to become a net importer of the grain.

Cries of hunger

But even as things stand now, Kenya is not in a position to adequately feed its people as is evident from the cries of hunger in various districts that have experienced drought this year.

If this trend continues, in a few years, there will be more fuel for people with cars, but not enough to feed the poor who eat ugali, githeri, muthokoi and other maize-based meals every day.

Just so you understand how serious the situation has become, Reuters recently reported that Mr Jean Ziegler, the UN special rapporteur on the right to food, called for a five-year suspension of biofuels.

According to him, it was "a crime against humanity" to convert food crops to fuel at a time when there were more than 850 million hungry people in the world.

But if what is happening now is not a good thing, how did countries begin to explore the possibility of using plant-based fuels in the first place?

You may remember that in the 1970s, global oil prices shot up, sparking fears of economic decline even in booming economies like Kenya's.

This happened at a time when agricultural products were fetching low prices in the world market. At the time, countries in which agriculture was "the backbone of the economy" as we used to say, started wondering why they were selling their crops cheaply only to buy fuel at high prices.

They started saying: Instead of selling such products for low prices to buy fuel, why not crush them to extract oil?

According to two Brazilian scholars, Emilio La Rovere and Andre Pereira, this is what happened in Brazil, where sugarcane was used to produce biofuel, "not only for the sake of coping with the oil shock, but also in order to deal with falling sugar prices".

Thirty years after the 1970s oil crisis, the high fuel prices are back and more countries are feeling the need to find alternative sources of energy. Now they are grinding maize, sugarcane and jatropha seeds to produce fuel.

In Kenya, this has not happened on a significant scale to influence pump prices, but it is threatening the food supply chain already because more land is being used to grow fuel rather than food.

According to Grunwald, this is one reason why food prices are rising. And the logic is simple. The supply of say, maize, is reducing at a time when demand is growing.

Only last week, Vice-President Kalonzo Musyoka said that the price of a bag of maize had gone up to Sh2,400.

Last year, the price was Sh1,500. But it is likely that even with the improved price, there is not enough maize because farmers have turned to alternative ventures -- jatropha, for instance.

So what are we to do to reduce hunger while coping with the rising fuel prices? Grunwald has a simple answer. He says: "Growing fuel is still an inefficient use of good cropland. Strange as it may sound, we're better off growing food and drilling for oil."