People who haven't had cancer might assume that those who have would take the opportunity to embrace their second chance and live as healthily as possible. But while those intentions might often be in the right place, it's another thing to successfully realise them.

A study in the US has found that many cancer survivors maintain poor diets and food choices after making their recoveries – worse than the diets of people who have never had cancer, in fact – highlighting the need for dietary intervention in what researchers say is a vulnerable population within the community.

"Cancer survivors are usually motivated to improve their health, so I think it is remarkable that they are still burdened by a sub-optimal diet," said Fang Fang Zhang, an epidemiologist at Tufts University and co-author of the study, as reported by Deborah Netburn at the Los Angeles Times.

The researchers compared the dietary intake of 1,533 cancer survivors with that of 3,075 individuals who had never had cancer. Viewed in light of the 2010 Dietary Guidelines for Americans, neither group scored particularly well in terms of nutritional intake, but the Healthy Eating Index score of 47.2 out of 100 for cancer survivors was lower than the 48.3 for those with no history of cancer. While there's not a huge degree of difference between the two poor scores, it's enough to have researchers concerned.

The study also found that cancer survivors consume less fibre and more empty calories than people who have not had cancer. Survivors have low dietary intake of vitamin D, vitamin E, potassium, and calcium, and consume too much saturated fat and sodium. About the only good thing you can say is that the diet of cancer survivors improves with age, with the oldest cancer survivors maintaining the healthiest food intake.

Among survivors, breast cancer survivors were found to have the best diets, while lung cancer survivors had the worst – and cancer survivors who currently smoke had worse diet quality than non-smokers or former smokers.

While the exact reasons for why cancer survivors are maintaining poor eating habits are unknown, it's possible that their experience in surviving a life-threatening illness has somehow altered their dietary intake for the worse.

According to Zhang, cancer treatments can cause people to experience food cravings or can alter the way foods taste, with the effects persisting long after recovery. Or high levels of stress resulting from the episode could affect diet or make it difficult to prioritise the right sorts of foods.

Of course, the reverse scenario is also true. Some survivors may have had poor diets to begin with – which in some instances could have contributed to their cancer – and despite medical advice for them to improve their nutrition, they may have been unwilling or unable to make the right changes.

Future research may provide the answers on causation, but in any case the results of the current study show that cancer survivors – a group that already faces higher risk of chronic health complications – need all the help they can get in getting their diets on track.

"Dietary changes that include more fibre, fruit, and vegetables in the diet and less fat, sodium, and added sugar would be important for cancer survivors," Zhang said in a press release. "Oncology care providers can play critical roles in reinforcing the importance of a healthful diet, and can refer patients to registered dieticians who are experts in oncology care or to other reputable sources in order to improve survivors' overall health."

The research is published in Cancer.