In recent years, the popular idea of reducing carbon footprints by eating locally to cut down food miles has come under close examination. However, a recent study published in Nature Food indicates that global food miles might account for as much as 20 percent of food-related emissions, a significantly higher percentage than previous estimations. This statement begs the question: Are food miles more significant than we initially believed?

Food miles represent the distance food travels from production to consumption, with previous studies suggesting that the emissions from these miles are tiny compared to the emissions produced during the food growing process. For instance, producing one kilogram of beef generates almost 99 kg of CO₂, while apples only produce 0.4 kg per kilogram. If the goal is to minimize dietary carbon footprints, it would be more beneficial to choose foods with lower overall carbon footprints, even if they have to travel a distance. Therefore, reducing meat and dairy intake could prove to be a more effective strategy.

The recent study doesn’t contradict (相矛盾) this conclusion. The reason why the reported proportion is higher is that the calculation includes all transport involved, including the transportation of fertilizers, farm equipment, and pesticides (杀虫剂). Hannah Ritchie, a researcher at the University of Oxford, suggests that a term other than “food miles” would be more appropriate to avoid any confusion. If the study had followed the standard definition of food miles, the per-centage would drop to 9 percent, which corresponds more closely with the 4 to 6 percent found in prior research.

Moreover, the study theorizes that even if all food was produced in the countries where it is consumed, the reduction in emissions would only be 1.7 percent overall. This is due to the fact that a larger proportion of food would be transported by road rather than by sea, with trucks producing higher emissions per ton of cargo than ships.

“So, overall, the bottom line is still that what you eat has a much bigger impact on emissions than the distance that food has to travel to reach you,” said Ritchie.

Food shopping has become a dangerous pursuit. Ready-meals are packed with salt and preservatives (防腐剂), breakfast cereals are sweeter than chocolate bars, and processed meats are packed with nitrite-preservatives, which can form harmful compounds when cooked. A new term is catching on to describe these nutritional bad guys: ultra-processed foods (UPFs). Just how bad are UPFs, and what do they do to us?

In his new book, “Ultra-Processed People”, Chris van Tulleken, a doctor and television presenter, argues that UPFs dominate the food supply in rich countries, and are also creeping into diets in low-and middle-income countries.

The concept of UPFs was put forward by Carlos Monteiro, a Brazilian scientist, in 2009.His team observed that although people in Brazil were buying less sugar and oil, rates of obesity and type-2 diabetes (糖尿病) were rising. That was because they were instead eating more sugar, fats and additives in packaged snacks and pre-made meals.

UPFs often go through many complicated industrial processes. That does not make them all unhealthy — a soya-based meat substitute can be part of a balanced meal — but the frequent consumption of UPFs causes a series of issues. Arguably, some UPFs are more alike to industrial products than food. There is plenty of evidence linking many ingredients in UPFs, such as sugar, salt, and saturated fats (反式脂肪), to negative health outcomes.

Yet UPFs are cheap, tasty and abundant, and for those on a tight budget or on specific diets, such as vegan (严格素食主义者), there are often few available alternatives. It is possible to eat well by selecting the right UPFs, such as whole-grain cereals. Government scientists at the American government’s Agricultural Research Service showed it was possible to build a health y diet with 91% of calories from selected UPFs. But Marion Nestle, a professor of nutrition at New York University, criticised the study, saying the researchers had a conflict of interest through their links to the food industry. Better stay cautious in those tricky supermarket walkways.

Cleaning your plate may not help feed hungry children today, but the old advice of mothers everywhere may help reduce food waste from the farm to the fork, help the environment and make it easier to feed the world’s growing population.

Hard data is still being collected, but experts in Chicago say about 30% to 50% of the food produced in the world goes uneaten. The average American throws away 33 pounds of food each month—about $40 worth, which means each person throws away almost 400 pounds of food every year. The US Department of Agriculture says that 23% of eggs and an even higher rate of produce end up in the trash(垃圾).

“We forget we have all these fresh fruit—and vegetables, and at the end of the week we have to throw them away,” said Esther Gove, a mother of three young children in South Berwick, Maine. “Now, I don’t buy as much fresh produce as I used to.”

But the effect of food waste arrives far beyond the kitchen. Agriculture (农业) is the world's largest user of water, a big consumer of energy and major emitter of greenhouse gases during production. Experts say reducing waste is a simple way to cut stress on the environment and can ease pressure on farmers, who will be called on to feed an expected 9 billion people around the world in 2050, compared with about 7 billion today.

No matter how sustainable (可持续的) farming is, if the food’s not getting eaten, it’s not sustainable and it’s not a good use of our resources. In richer nations, fruit and vegetables end up in the trash because they aren’t pretty enough to meet companies’ standards, and have gone bad in a home refrigerator or aren't eaten at a restaurant. In developing countries, much food goes wrong before it gets to the market because of poor roads and lack of refrigeration. High food prices are another reason, because some people can't afford the food that's produced.