Gained weight? Blame climate change! Higher CO2 levels are making our food more calorific and less nutritious, study finds

If you've piled on the pounds recently, a surprising factor could be to blame climate change. That's according to scientists in the , who warn that higher levels of carbon dioxide (CO2) in the atmosphere are making critical crops like rice and barley more calorific and less nutritious. CO2 increases calories by boosting photosynthesis, which produces more sugars and starches in crops. However, this surge decreases the concentrations of protein and nutrients leading to a higher calorie food with lower overall nutritional quality. The team from Leiden University warn of a 'pervasive elemental shift' across a wide range of popular edible plants. 'Nutrient security is under threat even if food security remains adequate,' they say. 'Food will become more caloric and less nutritious.' As a result, humans will suffer higher rates of obesity, weakened immunity and more chronic diseases, according to the team. For their new metaanalysis, researchers analysed and compared data from different studies where crops were grown at various CO2 levels, both indoors and outdoors. They looked at 43 edible crops in total, including rice, barley, potatoes, tomatoes, wheat, soybeans, peanuts and lettuce. According to the analysis, when the CO2 level doubles, so too does the detrimental effect on the nutrients in the crops. On average, essential nutrients such as zinc, iron and proteins decrease by 4.4 per cent, while some decrease by as much as 38 per cent. Chickpeas were found to have the most powerful and significant average change of a single nutrient (zinc), while wheat and rice the two most popular crops around thee world also suffer. The team warn: 'Rice is the primary staple crop for over half of the world's population, and another 2.5 billion people are dependent on wheat. 'Both show significant decreases in essential nutrients such as protein, zinc and iron.' At the same time, the number of calories per sample is increasing, which suggests obesity levels will rise, regardless of how much we consume or how much we exercise. The study also found concentrations of harmful substances such as mercury and lead may be increasing, although more data is needed to investigate this further, the team say. Overall, their findings suggest our food will become more calorific, less nutritious and more toxic in tandem with increasing greenhouse gas emissions. Regardless of how much we eat, spiraling emissions of the greenhouse gas could cause health problems simply because our food will lack nutrients, the study suggests. Humans may have to adjust diets in the future or find more space and equipment to grow edible crops in special conditions with more carefully controlled CO2 levels. Researchers warn that the effect of global CO2 rise is already reflected in the ambient CO2 levels compared with decades ago. Earlier experiments looked at as part of the study were conducted at CO2 levels around 350 parts per million (ppm), while modern experiments were conducted at around 415 ppm. 'We looked at what would happen at 550 ppm, a level we expect to reach in our lifetimes,' said study author Sterre ter Haar, an environmental scientist at Leiden University. 'We currently live at 425 ppm, so we're already halfway through this model.' Even if we have enough food to feed a growing global population, food will become more caloric and less nutritious. This will contribute to 'hidden hunger', where people have sufficient food calorically but insufficient nutrients. 'Decreasing nutritional value can have devastating health consequences, contributing to (further) malnutrition, including in previously sufficient populations,' the team say. The study, published in , also presents a concern for industrially grown food in CO2enriched greenhouses. Greenhouses can aid in improving dietary quality by increasing food diversity and availability, but the nutrient concentration of these foods 'should be included as an additional perspective', the scientists add.