T lymphocyte and cancer cell, SEM.

A cancer cell (green; artificially coloured) and an immune cell called a T cell. Obesity puts a strain on the body’s antitumour immune brigade. Credit: Steve Gschmeissner/SPL

Cancer

Why obesity can weaken the body’s tumour-fighting defences

Changes triggered by obesity help to give tumour cells the upper hand in the struggle for nutrients.

Excess weight can increase the risk of several diseases, including some cancers. Now, a study in overweight mice suggests that obesity’s effects help cancer cells to gobble fuel — depriving tumour-killing immune cells of energy.

Tumours consume fats, which serve as fuel for some immune cells that can recognize and destroy cancer cells. Arlene Sharpe and Marcia Haigis at Harvard Medical School in Boston, Massachusetts, and their colleagues fed mice a high-fat diet, which caused changes such as weight gain and increased blood levels of fatty molecules. Then, the researchers injected the rodents with cancer cells, which grew into tumours.

The high-fat diet reduced the number and activity of cancer-killing immune cells inside the tumours, accelerating cancer growth. Additional experiments provided an explanation: when fat molecules are plentiful, cancer cells use them up, starving immune cells and reducing their activity.

The authors also genetically engineered cancer cells to prevent them from making use of fats. In mice eating high-fat diets, treatment with these altered cells led to reduced tumour growth compared with an infusion of standard cancer cells.