Compared to 50 years ago, today’s fruits and vegetables carry smaller amounts of some key nutrients, including protein, calcium and vitamin C, according to new study findings.

“This is one more reason to eat more fruits and vegetables,” lead author Dr. Donald R. Davis told AMN Health. “We have many reasons, but this is one of them.”

Although there is probably more than one explanation, the trend may be largely due to farmers choosing to breed higher-yielding crops, Davis said.

Plants have a fixed amount of energy they can spend, he said, and varieties with high yields may have less energy to take minerals from the soil and transport them around the plant or to synthesize vitamins and amino acids, which make up proteins.

“Yield is not everything, and there are trade-offs involved,” said the researcher, who is based at the University of Texas in Austin. “This is something we need to become aware of as a society.”

Previous research from the U.S. and United Kingdom has suggested the nutrient content of fruits and vegetables has declined in recent years. To investigate further, Davis and his team compared the amounts of 13 key nutrients in 39 vegetables, 3 melons and strawberries in 1950 and 1999.

The investigators found that, overall, vegetables and fruits contain less protein, calcium, phosphorus, iron, riboflavin and vitamin C today than in 1950. The amount of seven other nutrients was unchanged.

The amount of decline varied for different nutrients, the authors report in the Journal of the American College of Nutrition. For instance, protein fell by 6 percent, while riboflavin appeared to drop by 38 percent.

Davis said his group focused on declines in nutrients across vegetables and fruits overall, rather than on individual types of produce.

However, they found that celery, green peppers and tomatoes appeared to have lost the largest amount of protein, while phosphorus dropped most markedly in cantaloupe, head lettuce and tomatoes. Eggplant and tomatoes appeared to have lost the most vitamin C, he added.

SOURCE: Journal of the American College of Nutrition, December 2004.