If I am significantly overweight and want to lose weight, what should I focus on more at first: my diet or exercise?

If you are Significantly Overweight, then, assuming you do not have Hormone Issues (Thyroid etc), you ought to immediately Re-Plan your Nutrition.

 

Hormone Issues

In case you do have Hormonal Issues that need to be worked out, please seek appropriate medical help, ASAP.

 

Nutrition

The following will definitely help with Nutrition (Re)Planning and Control:

1) Do NOT skip Breakfast

2) Include a Good Amount of Quality Protein with ALL your Meals

3) Do NOT forget your Carbs and Fats, but go easy with the amounts

4) Ensure Portion Control (Eat Less overall)

5) Ensure a Calorie Deficit overall (Calories In is Less than Calories Expended)

6) Have a 3-5 hour Gap between Meals (NO SNACKING ON ANYTHING IN-BETWEEN)

7) Have Dinner as Early as Possible…definitely, 3 hours or so before going to sleep

8) Have a 10-12-14 hour Gap between Dinner and Breakfast the Next Morning (NO SNACKING ON ANYTHING IN-BETWEEN)

The above will have a SIGNIFICANT impact on your Excess Fat Loss.

Please Note: In case you are Diabetic and take Medicines to Control it, you need to be Extra Vigilant about your Blood Sugar Numbers, to ensure that you do not get Hypo Glycemic (Low Blood Sugar). This is VERY IMPORTANT.

Exercise

Exercise will help with getting you more Fitter and Healthier and will also of course, help with Excess Fat Loss. Will help with increasing your Metabolism (Calories are Expended more than they are Stored as Fat). Will help you Put on more Muscle, Improve your Cardiovascular Health, Improve your Flexibility, Improve your Bone Density and with many other Good Things.