The cutbacks by the World Food Program were necessary because of a lack of resources, the WFP and the U.N. Refugee Agency announced in a statement Thursday.
"We have done everything possible to avoid this, but it has become necessary to reduce ration sizes by 20 percent in November and December in order to stretch our existing food stocks to last through the end of the year," said Ronald Sibanda, WFP country director for Kenya.
The reductions will affect an estimated 535,000 inhabitants of the Dadaab and Kakuma refugee camps.
Sibanda said the reductions were "temporary" until pledged donations arrive in 2014. A donation of $20 million from the United States is expected to provide for distribution of food in March, but WFP said it would need $20 million more to cover the gap in January and March.
WFP needs about $10 million a month to distribute more than 10,000 metric tons of food to refugees in both camps, the statement said.
With the reductions, refugees will get 1,680 kilocalories a day rather than the recommended 2,100 kilocalories, said WFP.
The camps were established more than 20 years ago.