Have your thyroid function checked.
You need to know your exact TSH value, don't just accept that your function is in the normal range, as that goes to 4.5 abut over 2.5 can by hypothyroid.
As to diet, a nutrient dense diet is the most scientifically valid, and uses the types of foods that prevent excess weight [and that is not animal foods a la atkins].
See the book, EAT TO LIVE by doctor Joel Fuhrman for this diet.
Resistance weight training, walking everywhere you can, and aerobics 3 times a week are all needed.
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