The low(er) carbohydrate group had more muscle, which translates into a higher metabolism. They also, by nature of the diet, avoided highly processed foods.
The high-fat group followed something of a modified Atkins diet. They were told to eat mostly protein and fat, and to choose foods with primarily unsaturated fats, like fish, olive oil and nuts. But they were allowed to eat foods higher in saturated fat as well, including cheese and red meat.
The low-fat group included more grains, cereals and starches in their diet. They reduced their total fat intake to less than 30 percent of their daily calories, which is in line with the federal governmentÃ(TM)s dietary guidelines.
The low carbohydrate group ate more protein, which is essential to maintaining muscle. Also, knocking out "cereals and starches" probably knocked out highly processed grains and sugars. I think it's not so much what they're eating but what they're NOT eating: highly processed CRAP.
Lookup Clarence Bass. The guy looks GREAT at 75 and has maintained (and written about) a moderate diet and exercise plan since 40. I'm nearly 40. I love being active. I've competed in many sports including soccer, football, track and bodybuilding. I still have a good metabolism, good muscle mass and low body fat. Through variations of my diet I've found that a moderate diet including unprocessed or minimally-processed and uncooked foods is the best diet for me. Whole milk, nuts, avocados, fruits, brown rice, beans, salmon, lean beef or turkey, steamed broccoli, etc. A low carbohydrate diet makes me weak. I can't muster the explosive energy for an intense exercise session while carbohydrate depleted. When in ketosis (completely carb depleted), my breath smells like alcohol, my joints ache, I'm irritable and generally feel like crap. Maybe I'm different. My favorite pre-workout meal is a bowl of rice about an hour before. Carbs are fine. Just not the super-processed stuff.