The North has relied on foreign handouts since the late 1990s when it suffered a massive famine that was estimated to have killed 2 million people. North Korea also suffered from devastating floods earlier this year, which experts have said may worsen the country's food shortages.
Katharina Zellweger, who led the Swiss Agency for Cooperation and Development in Pyongyang for five years until September, said North Korean children need a balanced diet, though the public rationing system has been very up and down.
She said rations fell to 150 grams per day during the "barley season" in late spring and early summer, before the fall harvest, noting 150 grams is equal to about 360 calories.
"The average western diet tops around 2,000 calories per day. 150 grams is the equivalent of a hamburger and a Mars bar," she said in an interview with Yonhap News Agency in her office in the Asia Pacific Research Center of Stanford University.
She said she fears for the next generation because the effects of malnutrition are permanent.
On average, North Korean children are much shorter than their South Korean neighbors of the same age, due to poor diet, according to aid officials.
The World Food Program has said that a third of all North Korean children under five are chronically malnourished and that many more children are at risk of slipping into acute stages of malnutrition unless targeted assistance is sustained.
She also said food aid should be detached from politics, noting what is needed is planned food interventions.
There have been widespread allegations that the North diverts outside food aid to its elite and military, a key backbone of North Korean leader Kim Jong-il's rule.
She said the North's economy, at least in Pyongyang, is improving, citing emergence of markets, money, mobile phones, motorcars, and a middle class. She did not give further details.