YAOUNDE (Reuters) - "Is it not said 'A hungry man is an angry man'?" commented Simon Nkwenti, head of a teachers' union in Cameroon, after riots that killed dozens of people in the central African country.

It is a proverb world leaders might do well to bear in mind as their impoverished populations struggle with food costs driven ever higher by record oil prices, weather and speculators trading in local market places and on global futures exchanges.

Anger over high food and fuel costs has spawned a rash of violent unrest across the globe in the past six months.

From the deserts of Mauritania to steamy Mozambique on Africa's Indian Ocean coast, people have taken to the streets. There have been "tortilla riots" in Mexico, villagers have clashed with police in eastern India and hundreds of Muslims have marched for lower food prices in Indonesia.

Governments have introduced price controls and export caps or cut custom duties to appease the people who vote for them, but on streets across Africa, those voters want them to do more.

Sub-Saharan Africa is particularly vulnerable: most people survive on less than $2 a day in countries prone to droughts and floods where agricultural processes are still often rudimentary.

For African households, even a small rise in the price of food can be devastating when meals are a family's main expense.

"People have been driven to destruction because they no longer know what to do or who to talk to," said Ousmane Sanou, a trader in Patte d'Oie, one of the areas worst hit by February riots in Burkina Faso's capital, Ouagadougou.

"They understand it's the only way to get the government to change things. Prices must come down -- otherwise we're heading for a catastrophe."

Over 300 people were arrested in some of the worst violence for years in normally calm, landlocked Burkina, prompting the government to suspend custom duties on staple food imports for three months -- measures some other countries have also taken.

But unions have threatened to call a general strike in April unless prices fall further.

Anger over rising prices also fuelled violence in Mauritania late last year. And at least six people were killed when taxi drivers in Mozambique rioted over fuel prices in February.

In Senegal, police raided a private television station last Sunday after it repeatedly transmitted images of police beating demonstrators with electrified batons and firing tear gas during an illegal protest over high food prices in the capital Dakar.

The poor country on Africa's west coast witnessed the worst rioting in more than a decade last year, as hundreds of youths smashed windows and burned tires in anger at high prices and government efforts to clear away street traders.

MARKET FORCES

The U.N. World Food Programme (WFP) says staple food prices in some parts of Africa have risen by 40 percent or more in six months. And this on a continent where malnutrition rates in some areas regularly top emergency levels even in an average year.

Food inflation in Africa is 2.8 percentage points higher than headline inflation, the International Monetary Fund (IMF) said this month.

In South Africa last week, central bank Governor Tito Mboweni warned consumers to "tighten their belts" as the targeted inflation measure reached a five-year high at 9.4 percent year-on-year in February, from 8.8 percent in January.

Already, consumer spending has slowed sharply, and confidence levels are at multi-year lows -- all this on top of chronic energy shortages in Africa's biggest economy.

In Cameroon, a taxi drivers' strike over rising fuel costs -- caused by many of the same factors pumping up food prices -- triggered widespread rioting exacerbated by anger over the cost of food, high unemployment and plans by President Paul Biya to change the constitution to extend his 25-year rule.

Government ministers said around 25 to 40 people were killed, although a human rights group put the toll at over 100.

The rising food prices have affected both Africa's small middle-class, like consumers in resource-rich South Africa, and poorer people like Sanou, the trader in Ouagadougou.

While famines like those witnessed in the 1980s are less common now thanks to aid and development programmes, there is the risk of a return to chronic inflation which could threaten the relative economic stability achieved by many African states.

"We are frustrated. We are disgruntled," said Jean-Martin Tsafack, a 32-year-old law graduate who sells imported second-hand clothes in Cameroon's capital Yaounde.

"Some of us have become hawkers, others truck pushers (barrow boys). Many girls who were my classmates in university have now become prostitutes just to have something to eat. Life is becoming unbearable," he said.

GLOBAL ISSUES

There are several reasons for the spiraling cost of living. Record oil prices driven by strong demand and insecurity in major production areas have pushed up fuel pump costs, making anything that has to be transported to market more expensive.

Rising consumption of livestock fodder and other foods by fast-expanding China and India, and the use of land and crops for biofuels have boosted demand. Erratic weather, perhaps due to climate change, has trimmed harvests in some growing regions.

Meanwhile, investment funds and other speculators have bet on prices to continue up in a self-fulfilling cycle.

Across the world, governments are facing the consequences.

Philippines President Gloria Macapagal Arroyo asked Vietnam earlier this year to guarantee Manila up to 1.5 million tonnes of annual supply of rice because of fears that shortages later this year could spell political trouble for her.

Indonesia, where President Susilo Bambang Yudhoyono is expected to seek a second term in office next year, has unveiled new measures to stem rising prices, targeting palm oil-based cooking oil, wheat flour, rice and soybeans.

And in just one example from Latin America, Peru said last week it would give away food to its poorest citizens and set up a fund to absorb high oil prices -- this as President Alan Garcia's approval rating has fallen to below 30 percent.

POLITICAL RISK

In Africa, countries like Mauritania, which imports 70 percent of its food, have been among the worst affected.

"I can't take it any more. I've stopped eating a meal in the evening," said Ami Gandega, 36, a civil servant in the capital Nouakchott.

The government suspended import tax on cereals last year and is bolstering village grain stores with subsidized stocks -- but aid workers believe this is not enough.

The WFP fears Mauritanian families will not only have to ration what they eat, but also cut back on education spending, sell livestock, or even send children to work or beg to survive.

"Inflation of staples is really out of control. We've never seen this before," said WFP representative Gian Carlo Cirri.

"If we don't react now, this summer will be full of danger."

WFP has forecast a "perfect storm" of woes for its operations: it is faced with a $500 million funding shortfall purely due to rising costs of buying and distributing food, even before taking into account greater need for aid now.

And that need is ever growing. Last week, 40 aid agencies urged the world to focus attention on Somalia's "catastrophic" humanitarian crisis where hundreds of thousands of people are suffering from war, drought and food shortages.

Some humanitarian workers fear the growing furor over rising prices could even encourage traders to hoard stocks.

Government reaction -- through cuts in duties or subsidies -- may slow down real economic adjustment to higher prices, such as encouraging local farmers to grow more. But they help cushion the blow for governments and the poor.

"There are very few governments, especially in this region, that are going to be strong enough to be able to encourage that normal economic incentive to come through over the course of time," said Standard Chartered Africa research head Razia Khan.

"Any measures to allow the price of imported food to be reflected at the consumer level will be very rapidly reversed."

So more and more governments in Africa may opt for food aid, especially subsidies, as recommended by donors like the IMF.

Perhaps, at the back of their minds, they will remember Liberian President William Tolbert, who was stabbed to death in 1980 in a crisis sparked by riots over a rice price increase.

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(Additional reporting by Mathieu Bonkoungou in Ouagadougou, Ibrahima Sylla in Nouakchott and Alistair Thomson in Dakar; Writing by Alistair Thomson; editing by Clar Ni Chonghaile)

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