Unfortunately, for energy state of the art is calorimetry for now. But relying on just "energy" or calorimetry is a terrible heuristic for energy uptake or nutrition/dieting.

I am not a nutritionist but I'd probably choose something akin to blood glucose over calories for food consumption.

If I had to go so simple I'd probably optimise for sugar reduction. And after that carbohydrate reduction.

You'll find you can eat a lot of food and food will be filling if you have a pseudo keto diet. You have to work so much harder to get your calories and fats (when not mixed with sugar) is much more satiating.