The increasing evidence of the beneficial effects of long-term dietary intervention may signal an exciting future in the prevention of the world’s most prevalent mental disease – depression – through healthy diet.
Studies of dietary pattern and depression consistently point to reductions in depression among people who consume a Mediterranean diet, which is high in healthy fats, fruit and vegetables and fish, according to Prof Miguel A Martínez-González of the University of Navarra, Spain, who says there is now a need for wider trials in this field.
Speaking at the annual conference of the Nutrition Society, which was held recently at University College Cork, Martínez-González pointed out that Finland has the highest rate of suicide in the world and Greece, Portugal and Italy the lowest.
“There is new evidence of a higher risk of depression in young and older adults where their predicted risk of cardiovascular disease is high. The baseline risk factors predict not only heart disease but depression, which suggests there is something linking both, and it may be diet,” he said.
In his research at the University of Navarra, Martinez-Gonzalez has shown a reduction in the incidence of depression in people who consume between 20g and 28g of olive oil a day. He has also shown that the risk of developing depression is 42 per cent higher in people who have a high intake of trans fatty acids from fast food and commercial baked goods.
Alcohol in moderation
In addition, moderate amounts of alcohol have been shown to prevent heart disease. The Spanish researchers have also found that moderate daily consumption of wine in older adults may also reduce the risk of depression.
Their studies have shown a reduced risk of depression in people on a Mediterranean diet with a high consumption of monounsaturated fats (mainly olive oil), fruit and vegetables, legumes, cereals and fish, and moderate amounts of meat, dairy and alcohol.
“Our findings replicate other studies of dietary pattern and depression,” said Martínez-González. “It is a relatively consistently strong finding, but we need further strong evidence from randomised control trials. I think the future is open for the exciting field of the prevention of depression with healthy diet.”
Sugar is not poison
People to “get real” when it comes to diet, said Prof Tom Sanders of King’s College in London.
“In the past year or so, there has been a lot of media attention on sugar, and talk about the end of the war on fat, and about fish oils being so wonderful for everything,” he said. “Foods with low glycaemic index are seen as good and sugars are bad. [But] sugar is not poison, nor as addictive as cocaine; that’s nonsense. I think it’s silly that sugar is described as a toxic substance when we synthesise it naturally. Even cows get sugar from the grass they chew.”
The real concern around sugar, Sanders said, was the increase in tooth decay, particularly in under-fives in the UK, which he suspects may be largely linked to sugary drinks being given in sippy cups.
When it comes to obesity, he said the biggest culprits were sugar-sweetened beverages – of which teenagers are the biggest consumers – and the increase in “munching” on fat-laden foods such as muffins, biscuits and crisps.
“I definitely think there are issues around the advertising and promotion of sugary foods and drinks,” he said. “People are being encouraged to munch all the time on sweets, crisps and sugary drinks. They are everywhere.
“Obesity has become a real problem in the UK and Ireland, and the real worry is that fat [people] are getting very fat. But the evidence does not support either fat or sugar as the main culprit: it’s the amount of food we are eating overall and the upsizing of portions.”
The bottom line for people who want to lose weight is that they have to restrict both carbs and fat – but not to unrealistic limits, as we need both for energy, according to Sanders. Sanders also notes that faddy high-protein or Palaeolithic diets are “okay for dogs but not suitable for humans”.
Increasing the risks: Obesity ‘accounts for a lot of new cancer cases now, and will into the future’
The daily reality for cancer surgeons today is to see obesity, diabetes and cancer side by side in patients undergoing surgery, Prof John Reynolds of Trinity College Dublin told the Nutrition Society.
The World Health Organisation predicts that Ireland is on track to become one of the most obese countries in Europe. Reynolds pointed out that the the link between obesity and cancers has now become “prime time” news.
“Compared to the link between smoking and lung cancer – with smokers having a 25-fold increased risk of lung cancer – the link between obesity and cancer is a lot less, at a twofold risk. But there is a considerable amount of obesity in society and it’s an increasing problem unless something is done.”
Research into the link between obesity and cancer is very much in its infancy and Reynolds’s team are involved in studies into the stomach and liver fat of obese patients.
“We need good public health policies to prevent obesity in the first place,” he said, “and we need to deal effectively with patients who are very obese by medical means and bariatric surgery.
“There is emerging evidence that bariatric surgery will decrease the likelihood of cancer in the future for obese patients. The country needs to step up to the plate in the treatment of obese [people] to reduce the prevalence of cancer in the future,” he told the conference.
Prof Helen Roche of University College Dublin addressed the conference about the use of personalised nutritional interventions to improve insulin sensitivity in overweight and obese adolescents.
Her study involved giving teenage participants a cocktail of nutrients not normally found in the poor diets of people who are overweight and obese.
Although the teenagers stayed the same weight, their insulin sensitivity and glucose metabolism improved, reducing their future risk of Type 2 diabetes.
“Some people respond well to supplements, while others might respond better to physical exercise, depending on their metabolism and other factors,” said Roche.
“We are trying to find biomarkers to [identify] who will respond best to what intervention. If we could do this, we could potentially prevent obesity in kids and adults.”
She made the point that her study was a proof of concept and more research was needed in this area.
“Of course, losing weight would be the best thing for those who are overweight and obese,” she said. “But losing weight and keeping it off are very hard, so we are looking at ways of improving the metabolism of those who are already obese to reduce their future risk of diseases such as type 2 diabetes, cardiac disease and cancer.”
