Unfortunately simply eating less calories than you burn doesn't necessarily lead to weight loss. You see the body is a clever bugger and if it triggers starvation mode it will lower the Basal Metabolic Rate so if you used to burn 1700 calories a day by existing that may go down to say 1500. So you stop being in calorie deficit and in fact when you go back to eating normally the BMR won't go back up. A huge reason why most people on radical weight loss schemes due to strict calorie control pit it all back on.
This is where the body has been using primarily carbs converted into Glycogen for energy.
The reason low carb diets such as Keto work is they train the body to become fat adapted and use fat for energy. So with the same calorie deficit the body that has been conditioned to use fat as an energy source simply continues to do so by using stored body fat. This keeps BMR up and the weight comes off. Very important to eat enough protein though as one of the reasons BMR goes down on low calorie carb based diets is because the body will break down muscle for energy. Keep muscle mass up by eating enough protein and make the body use body fat as an energy source and you are laughing.
I noticed also on keto my mid distance running performance was vastly improved - I literally had tonnes of energy and at 42 years old and down to around 98 kilos (181 cm height) but 8 months previously at 135 kilos I was doing a 10k run in 48 mins no problem whatsoever and not even slightly tired. The flip side is weight training on keto is a barsteward - performance is way down on a carb diet due to lack of glycogen to power the muscles.
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