Here are the best-fitting words for each gap:

1. C. main
2. C. energy
3. D. concentrate
4. A. lose
5. B. into
6. A. skipping

The complete passage would read:

"Breakfast is the (1) **main** important meal of the day. It provides the nutrients your body needs for good health, the calories it needs for (2) **energy** and helps to maintain your blood sugar level. Studies have shown that people who don’t have breakfast have a low blood sugar level and are often slow, tired, hungry and (3) **concentrate**. Surprisingly, breakfast actually plays a part in weight control. It’s easier to (4) **lose** weight if you eat in the morning rather than later in the day. Dividing the day’s calories (5) **into** three meals helps take off weight more efficiently than (6) **skipping** breakfast and having two larger meals a day does."