A large and growing share of Americans are obese, a phenomenon many health experts are calling an epidemic. Since the late 1970s, the share of adults in the United States who are obese has grown from 15% to 42%, and the similar share of children has grown from 6% to 20%.

Obesity imposes large costs on our health care system as it contributes to heart disease, stroke, diabetes and many other ailments.

Congress should investigate whether federal food subsidies are feeding the epidemic before it reauthorizes the giant Supplemental Nutrition Assistance Program in this year’s farm bill. SNAP — the food stamp program — subsidizes food consumption for 42 million low-income Americans.

The program’s cost has exploded from $63 billion in 2019 to $145 billion this year.

Subsidizing low-income food intake is a peculiar policy given that low-income adults and children are more obese, on average, than other Americans. Even within the low-income population, SNAP recipients are more obese than nonrecipients.

The U.S. Department of Agriculture, which runs SNAP, found in a 2021 study that adult men on the program had a higher obesity rate (37%) than low-income nonrecipient men (32%), while adult women on the program had a higher obesity rate (52%) than low-income nonrecipient women (40%).

The reasons for these higher obesity rates are not fully understood. Since the 1970s, average daily calories have risen about the same percent for low-income and other Americans, although the types of calories vary. When food stamps were created in the 1960s, low earners suffered from insufficient food, but today they consume too much unhealthy food.

SNAP benefits can be used to buy virtually any food in grocery and convenience stores except alcohol and food for on‐​premises consumption. A 2016 USDA study found that 23% of food purchases by SNAP households were sugary drinks, desserts, salty snacks, candy, and sugar, which can be called junk food. With SNAP spending of $145 billion this year, that means $33 billion in junk food subsidies.

On average, SNAP recipients have less healthy diets than other Americans, including low-earners not on SNAP. The 2016 USDA study found, for example, that 9.25% of food purchases by SNAP shoppers were sweetened beverages, such as cola, compared to 7.1% for non‐​SNAP shoppers.

A 2018 USDA study compared food purchases by SNAP households to lower‐​income non-SNAP households. SNAP households “acquired 31 percent fewer total vegetables, 40 percent fewer dark green vegetables and beans, 24 percent fewer whole fruits, 20 percent fewer whole grains, and 27 percent fewer seafood and plant proteins for every 1,000 calories acquired.”

For obesity, the problem appears to be not just how much we eat but also what we eat. For decades, the government advised Americans to eat carbohydrates and to deemphasize protein and fat. The USDA’s famous food pyramid featured six to 11 servings of bread, cereal, rice, and pasta, but just a small two to three servings of meat, fish, beans, eggs, and nuts.

Some nutrition experts now think that the government’s advice was off-base, and that rising carbohydrate intake is an obesity driver. USDA data shows that for all individuals average daily carbohydrate intake is up 22% since the late 1970s, fat is up 12% and protein is unchanged. For low-income individuals, carbohydrates are up 26%, fat is up 11% and protein is down 3%.

A USDA website says that “poor nutrition is a leading cause of illness in the United States, associated with more than half a million deaths per year,” but the agency’s largest program, SNAP, delivers poor nutrition. The SNAP program itself warns people not to consume sugary drinks, yet sugary drinks are the most popular food item purchased by recipients.

SNAP’s approach of subsidizing total caloric intake makes no sense in a population struggling with obesity. One reform would be to end subsidies for cola and other junk foods, as Florida Republican Senator Marco Rubio has proposed.

An alternate reform would be to replace the subsidize-all-foods method of SNAP with a fruits-and-vegetables-only program, which would save taxpayers about $100 billion a year.

However, the best reform would be to phase out federal SNAP altogether and allow states to fund their own food programs. Low-income nutrition is a complex problem and would be better tackled by diverse state approaches.

Numerous states have sought USDA waivers to ban junk foods from SNAP, but the USDA has rejected all such requests even though the current “anything goes” program has failed on nutrition.

The USDA’s SNAP website says that the program allows people to “afford the nutritious food essential to health and well-being,” but nutritious food is not what SNAP provides. It is time to end the failed national program and allow the states to find better solutions for both recipients and taxpayers.