When you are physically active, your body primarily burns carbohydrate and fat, and your muscle mass is maintained or maybe even increased.
This was effectively demonstrated in a study of overweight people who lost 8-10 percent of their body weight, while increasing their muscle mass by a few percent.

A study of mice who were supplemented with CLA (conjugated linoleic acid) for six months demonstrated that CLA helps reduce the age-related loss of muscle mass. The mice that got CLA had higher energy turnover in their muscle cells, and the supplement also stimulated certain antioxidant enzymes that protect cells.

Both studies are mentioned in American Journal of Clinical Nutrition in 2004 Jun; 79 (6): 118-25

Other studies show that CLA:

• Increases insulin sensitivity and steps up the energy turnover
• Helps carry fat to the energy metabolism inside muscle cells
• Prevents the uptake of fat in fat cells
• Helps build muscle mass/reduces age-related loss of muscle mass
• Improves the balance between fat and muscle tissue

CLA is a fatty acid that occurs naturally in meat (from ruminants) and dairy products (especially those with a high fat content)

Optimal concentrations of CLA are found in animals that have grazed on free land so that their intestinal bacteria can convert LA (linoleic acid) to CLA (conjugated linolenic acid). Altered feeding routines and living conditions in general have resulted in meat and dairy products with far less CLA. Low-fat dairy products and meat also contribute to the reduced CLA intake level.

You can take CLA as a supplement. If you want the optimal effect, you should combine it with exercise

It is a good idea to push your limits every now and then and be out of breath. This increases your cardiovascular fitness and your muscle mass. Please note that muscle mass weighs around 22 percent more than fat tissue. Physical training can help you obtain a figure that is better looking, slimmer, and more firm – but it will not necessarily show on the bathroom scale.

Remember to combine your exercise with healthy food. Low-fat diets and no physical activity can actually harm you