Final answer:
Low-income adults benefited the most from the Medicaid expansion under the Affordable Care Act, which included able-bodied adults under 65 with incomes at or below 133 percent of the federal poverty level.
Step-by-step explanation:
The group that benefited the most from health insurance coverage due to Medicaid expansion under the Affordable Care Act (ACA) is low-income adults. Prior to the ACA, Medicaid was limited to poor families, with many low-income individuals without children not qualifying. The ACA's expansion of Medicaid eligibility included able-bodied adults under 65 who earn no more than 133 percent of the federal poverty level. Although a large number of children were already enrolled in Medicaid, the expansion particularly targeted the inclusion of more adults into the program.
As of 2014, approximately 69.7 million people were enrolled in Medicaid, with almost half being children, but adults represent the second largest group enrolled at 28%. These expanded guarantees helped encourage those on welfare to join the labor force. However, it's important to highlight that even though a significant portion of Medicaid enrollees are children, the largest share of Medicaid spending goes towards seniors and people who are blind or have a disability, which together account for 64% of all Medicaid spending.