I'm guessing he's referring to the fraction of underweight children, 5.1% below the poverty line and 5.7% above 4x the poverty line.
Not sure whether 4x should qualify as "rich", but more importantly, being underweight is pretty low bar. For example, I am underweight.
The actual number as reported by USDA is 1%. The keyword to look for is "very low food security", formerly known as "food insecurity with hunger", which is the lowest range of food security measured by USDA. (The second lowest range, "low food security", formerly "food security without hunger", means poor diet but no reduction in food intake. Note that even among the "very low food security" households less than half reported "lost weight" and less than a third reported "did not eat the whole day".)
One interesting observation: "Typically, households classified as having very low food security experienced the condition in 7 months of the year, for a few days in each of those months." I'll go out on a limb and hypothesize that these few days are the last few days of each month. So one thing to try to reduce that number would be making welfare payments daily, instead of monthly. (I read that welfare these is delivered electronically, you carry a special card which looks like a credit card and a certain amount appears on it the first day of each month. So it shouldn't add any overhead to switch to daily installments.)
http://mchb.hrsa.gov/chusa11/hstat/hsa/pages/221oo.html