They can have a diet rich in vitamins and minerals and still be malnourished.
Obesity is a form of malnourishment.
Don't let this form of malnutrition push you into an uncomfortable medical condition or rob you of the fun of retirement years. I define the normal weight in women as 114 lbs. In men you just change the baseline to 124 pounds. There are more complex formulas, but I can do this one quickly in my head. Here, as in many areas, prevention is better than cure.