COLUMBUS, Ohio -- The type of fat in avocadoes not only helps the body absorb carotenoids such as beta-carotene, but it also helps convert them to vitamin A -- a vital function that could reduce severe vitamin A deficiencies in the developing world.
That’s according to a recent Ohio State University study that found that the body formed more than 12 times as much vitamin A from carrots when they were eaten with avocado than when they were eaten alone. Similarly, more than four times more vitamin A was formed from tomatoes when they were eaten with avocado in the study, which was published Aug. 1 in the Journal of Nutrition.
“From previous studies, we expected to find an increase in absorption of provitamin A, and we did,” said lead author Rachel Kopec. “But our finding about the conversion to vitamin A is new, and pretty significant.” Provitamin A substances are turned by the body into active vitamin A.
Kopec, currently a postdoctoral researcher at the French National Institute for Agricultural Research, worked on the study as part of her Ph.D. at Ohio State under Steven Schwartz, professor of food science and technology and holder of the Carl E. Haas Endowed Chair in Ohio State’s College of Food, Agricultural, and Environmental Sciences. Schwartz also holds an appointment with the college’s research arm, the Ohio Agricultural Research and Development Center (OARDC).
Schwartz said the study advances previous work done in his lab.
“We are continuing to learn that consuming fat in the diet not only enhances the absorption of carotenoids and fat-soluble nutrients, such as provitamin A beta-carotene, but also increases the conversion and delivery of vitamin A,” Schwartz said.
According to the World Health Organization, vitamin A deficiency is a public health problem in more than half of all countries, particularly in the developing world. It is the leading cause of preventable blindness in children and increases the risk of disease and death from severe infections.
“This is one of the leading nutritional deficiencies in the world, and one of the most preventable,” Kopec said.
Many of these countries, including Mexico and India, she said, have the proper climate to grow avocadoes.
People can get vitamin A directly from some foods, such as liver and other organ meats, eggs, and foods fortified with the vitamin, including milk and breakfast cereal. But the body can also be supplied with vitamin A from foods high in some types of provitamin A carotenoids, such as alpha-carotene and beta-carotene, found in carrots, tomatoes, dark-green leafy vegetables, and other red, yellow and orange vegetables.
For the study, Kopec’s team recruited two dozen healthy people to eat test meals and have their blood tested during two daylong visits to the clinic. They were asked to abstain from eating foods rich in vitamin A and carotenoids for two weeks beforehand.
Early in the day, study participants were given either tomato sauce made from a unique variety of orange hybrid tomatoes high in beta-carotene, served with or without sliced avocado; or a bowl of raw baby carrots, served with or without guacamole made from avocado.
The tomato sauce used in the study was made from tomatoes developed and grown by David Francis, a researcher at OARDC’s Wooster campus and professor of horticulture and crop science in the college. The avocadoes were provided by the Hass Avocado Board. They were the Hass variety, which has deep green, bumpy skin and is generally available in grocery stores, Kopec said.
“These meals weren’t everyone’s idea of a favorite breakfast, but they were palatable,” she said.
The participants were later given a lunch low in carotenoids, provitamin A and fat.
The participants’ blood was tested eight times, between two and 12 hours after eating the test meal, to study the extent of vitamin A formation. Two weeks later, the participants came back and ate the other test meal and went through the same round of blood tests.
Kopec said the fat from avocado, which essentially has the same lipid profile as canola oil, plays three roles in interacting with provitamin A substances. First, the fat helps the provitamin to be absorbed during digestion. Second, it helps form a package around the provitamin for its transfer through the bloodstream to the liver, where it can be converted to active vitamin A and be delivered to tissues or stored for future use. Third, it assists in actually converting the provitamin A to active vitamin A immediately after absorption.
Besides finding that avocadoes increase the immediate conversion of provitamin A from carrots by 12.6 times and from tomatoes by 4.6 times, Kopec’s team also found that it increased absorption rates: The beta-carotene from tomatoes was absorbed 2.4 times more when consumed with avocadoes. Carrots, which contain both alpha- and beta-carotene, did even better: Their alpha-carotene was absorbed 4.8 times more, and their beta-carotene was absorbed 6.6 times more, when eaten with avocado.
“As someone who loves to study fat-soluble compounds, I feel we’re helping to turn the page of the 1990s phenomenon of demonizing fats and replacing them in the diet with carbohydrates,” Kopec said. “We’re finding more and more evidence that it is important to include certain types of fat in a meal to be able to absorb these nutrients and make them active.”