I think the most common nutritional problem in adults is obesity which can lead to type 2 diabetes (among many other health issues).
People with type 2 diabetes, unlike type 1, actually produce insulin. Typically, they are not producing enough or their bodies are not using the insulin adequately. The disease can affect anyone, but the risk is much higher for those who are obese.
Medical experts agree that the number one factor affecting the development of type 2 diabetes is weight/nutrition control. The more fatty tissue the body has, the more resistant the cells become to insulin. Older people are at a high risk for developing this disease for a number of reasons. As people age, they tend to become less active. Also, the body changes dramatically as it ages. Changes in metabolism and hormonal levels make weight maintence even more difficult. Stress and time management often negatively affects weight. Because older people in general are at a high risk of obesity they are necessarily also at a high risk of developing type 2 diabetes.