This likely goes without saying, but when I was heavily overweight, I was also tired a lot. This was largely due to my unhealthy diet, which contained a lot of takeout, convenience foods, and way too much sugar. Sure, I ate vegetables and healthier, home-cooked meals even at my heaviest, but not nearly as much as I should have done.
I lost my weight following a ketogenic diet and will continue with this way of eating for the foreseeable future as I love the way it makes me feel. Ditching the starchy and sugary carbs and filling my plate with healthy fats, lean proteins, and lots of vegetables on a daily basis has, in combination with my weight loss, taken my energy levels to new heights.
I no longer have those mid-day slumps and I don't feel wiped out after a long day at work. Sure, I get exhausted sometimes when things have been particularly hectic — I'm only human, after all — but this happens way less frequently and I find myself bursting with energy more often than not.