Limits in medicine seem a contradiction in terms. Medicine advances continuously, shattering orthodoxies and opening new possibilities, some of which succeed spectacularly while others are mere incremental steps forward, overoptimistic dead ends, or (rarely) deceptive fabrications. The idea of a conference entitled “At the Limits” therefore seems entirely correct and a misnomer. Correct because debating knowledge on the edge of breakthrough is what medicine is about. Misnomer because, since medicine has no limit, one cannot be “at” something that does not exist. What one might say is that medicine is defined by a permanent transgression of boundaries around acceptable understanding. A systematic review recently argued that blood pressure should be reduced below the accepted limit of 140 mm Hg. The After Eighty Study found that aggressive intervention in older patients with non-ST-elevation myocardial infarction was more successful than conservative strategies. Medicine does live at the limits. Last week, Professors Derek Yellon and Lionel Opie convened their latest scientific symposium on Cardiology, Diabetes, and Nephrology At the Limits in London. It was a celebration of progress in understanding some of the most important diseases shaping outcomes for human life. And yet living at the limit isn't good enough. In too many ways medicine is failing those it claims to serve. Majid Ezzati and his colleagues (who make up the Non-Communicable Disease Risk Factor Collaboration) this month showed the extent of that failure. In a study of trends in obesity across 200 countries from 1975 to 2014, they found that by 2025 around one in five men and women will be obese. Although underweight remains an important concern in parts of Africa and South Asia, more people in the world are now obese (641 million) than underweight (462 million). Ezzati and colleagues conclude that, “Present interventions and policies have not been able to stop the rise in body-mass index in most countries.” In a second paper, Ezzati and colleagues looked at worldwide trends in diabetes. They estimated that the number of adults with diabetes rose from 108 million in 1980 to 422 million in 2014. Taken together, these findings suggest that global obesity and diabetes targets will not be reached. The story is considerably worse. Salim Yusuf's Prospective Urban Rural Epidemiology (PURE) study found that four important medicines for secondary prevention of cardiovascular disease—aspirin, β blockers, angiotensin-converting enzyme inhibitors, and statins—were unavailable or unaffordable for large numbers of people living in middle-income and low-income nations. Again, global targets for access to these life-saving medicines are likely to be missed. What accounts for this dismal performance? Some light was thrown on the answer to this question by Dariush Mozaffarian, Dean at Boston's Tufts Friedman School of Nutrition Science and Policy, who delivered the 2016 Lancet lecture at this year's At the Limits symposium. The Global Burden of Disease has found that diet is overwhelmingly the most important risk factor for illness in the US and globally. And yet you would never know this fact based on the seriousness with which nutrition is treated by academic medicine. Nutrition is hardly taught at medical school. It is not routinely captured in a patient's medical record. And nutrition interventions are almost never reimbursed. The field itself is riven with “passion and confusion”. There is a “cacophony of voices” claiming to know the secrets of the perfect diet. Yet few self-styled experts seem to understand the science of nutrition. Mozaffarian argued that current nutrition policy was at least 10–15 years behind the best nutrition science. An obsession with energy balance, calories, and fat is “insane”, he said. What matters is not quantity but quality. 800 calories of a nutritious diet is far better than 400 calories of a bad diet. He emphasised the value of a Mediterranean regime, one rich in nuts, olive oil, fish, fruits, vegetables, yoghurt, and whole grains. But even public guidance given by the respected US National Institutes of Health contradicts the best evidence. A lesson one might draw from Mozaffarian was that medicine, despite the pride it takes in its scientific status, remains deeply ideological. Physicians consistently ignore prevention science. Nutrition research is undervalued. And medicine seems comfortable allowing quacks and charlatans to prosper. Insane indeed.