Since we can’t spot reduce fat, the only way to ever get those flat abs is to burn body fat overall. For this reason, HIIT workouts, exercises that work multiple muscle groups simultaneously (like push ups, squat thrusters etc.), and weight lifting are going to be the most effective fitness strategies for bringing out your six pack because they are the most metabolic. Hours of cardio and tons of crunches are not the way forward here.

Noam Tamir, C.S.C.S, founder of TS Fitness, also says that metabolic resistance training and high-intensity interval training is a solid way to reduce fat all over, including belly fat. “These [types of exercise] help to burn calories during the workout, and they also give you that after-burn effect,” he says. “Plus, they help to change your body composition by increasing your muscle mass.”

Aging does play a role too. As you age, you lose muscle — especially if you're not physically active. Loss of muscle mass decreases the rate at which your body uses calories, which can make it more challenging to maintain a healthy weight. According to the 2015-2020 Dietary Guidelines for Americans, men in their 50s need about 200 fewer calories daily than they do in their 30s due to this muscle loss.
"Sleep is a cornerstone of weight management because of the impact it has on your hormones that control how you burn fat, how you store fat, and how you're maintaining muscle. The better your hormone balance, the better your weight management. I work my butt off to get eight hours a night, but right now I'm at six—the show is murdering me! Even if I go to bed early my son wakes up."

You don’t have to hop on the Paleo train and ride it all the way to the station, but increasing your intake of protein and reducing your intake of carbs is one of the fastest ways to lose belly fat without additional exercise. Protein helps to balance blood sugar and lower levels of insulin, a hormone that signals your body to store fat, especially around your midsection. For healthier carb alternatives, skip the white bread and pasta in favor of whole-grain complex carbs, seasonal fruits, root vegetables, and squashes.  Here are more foods that are proven to flatten your belly.
If it’s working for you I wouldn’t worry. I think health problems with low carb are slightly less of a concern in later years simply because there aren’t any hormones around to mess up. 🙂 I would simply be very cognizant of potential changes or symptoms – and if you start to notice weight gain, thyroid symptoms, etc while IF/carb cycling then it might mean it’s time to simply lighten up the IF and add in a few more carbs. you don’t need to eat HIGH carb but some relaxation of your guidelines, or playing with them a little bit, could be called for eventually (or now if you so choose) 🙂
Have Protein at Every Meal and Snack. Adding a source of lean or low-fat protein to each meal and snack will help keep you feeling full longer so you're less likely to overeat. Try low-fat yogurt, small portion of nuts, peanut butter, eggs, beans, or lean meats. Experts also recommend eating small, frequent meals and snacks (every 3-4 hours), to keep your blood sugar levels steady and to avoid overindulging.
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