In order to speak about a healthy lifestyle, you need the appropriate vocabulary.
Balanced/healthy diet - a combination of the correct types and amounts of food;

Calorie - a unit of energy, often used as a measurement of the amount of energy that food provides;

Crash diet - a way of losing body weight quickly by eating very little;

Diet - an eating plan in which someone eats less food, or only particular types of food, because they want to become thinner or for medical reasons;

Digestion - the process by which your body digests food, or your ability to digest food;

To be in a diet - to follow a diet;

To cut down on sugar/fat - reduce eating products with sugar/fat;

To do stretching exercises - to make your body or your arms and legs straight so that they are as long as; possible, in order to exercise the joints (= place where two bones are connected) after you have been in the same place or position for a long time;

To give up smoking/junk food - to stop smoking, eating unhealthy food;
To go to the gym/exercise class - to attend the place where you have physical activity; 

To injure - to hurt or cause physical harm to a person;

To lose weight - to become lighter;

To pull a muscle - to injure a muscle by stretching it too far so that it is very painful;

To put on weight - to become heavier;

To take vitamins - swallow useful tablets;

To warm up - if an event warms up, it starts to become more interesting, enjoyable, or exciting;

Vegetarian - a person who does not eat meat for health or religious reasons or because they want to avoid being cruel to animals;

He found calorie-counting the best way of losing weight.

I'm going on a diet next week and hope to lose ten pounds before Christmas.

Russell pulled a back muscle early in the game.

My friend is a vegetarian.