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Altering what we eat to conform to dietary guidelines would actually increase emissions of greenhouse gases, a study has found.

The researchers found that diet-related greenhouse gas emissions would increase by 12 per cent if dietary recommendations are followed.

And while the scientists aren't suggesting we should ignore dietary guidelines, they are suggesting that such guidelines should be made with more environmental considerations in mind.

The study is not a recommendation to eat less healthily, however, but rather to highlight the gap between food production and living sustainably. This pie chart from the researchers shows how greenhouse gas emissions of certain foods compare to the USDA dietary recommendations

Dr Martin Heller and Dr Gregory Keoleian of the University of Michigan's Center for Sustainable Systems looked at the greenhouse gas emissions associated with the production of around 100 foods.

They also looked at the potential effects of shifting Americans to a diet recommended by the US Department of Agriculture (USDA).

They found that if Americans adopted the recommendations in USDA's 'Dietary Guidelines for Americans, 2010,' but consumed the same number of calories diet-related greenhouse gas emissions would increase by 12 per cent.

Current estimates put the average American's daily calories intake at more than 3,300 calories a day. 

If Americans reduced their daily caloric intake to the recommended level of about 2,000 calories while shifting to a healthier diet, meanwhile, greenhouse gas emissions would decrease by only 1 per cent according to Dr Heller and Dr Keoleian. 

'The take-home message is that health and environmental agendas are not aligned in the current dietary recommendations,' Dr Heller said.

The paper's findings are especially relevant now because the USDA Dietary Guidelines Advisory Committee is for the first time considering food sustainability within the context of dietary recommendations, he said.

In its 2010 dietary guidelines, the USDA recommends that Americans eat more fruits, vegetables, whole grains, fat-free and low-fat dairy products and seafood. 

They should consume less salt, saturated fat, trans fat, cholesterol, added sugar and refined grains.

The guidelines don't explicitly state that Americans should eat less meat. However, an appendix to the report lists the recommended average daily intake amounts of various foods, including meat. 

The paper titled 'Greenhouse gas emission estimates of US dietary choices and food loss' was published in the Journal of Industrial Ecology. 

The recommended amount of meat is significantly less than current consumption levels, which Dr Heller and Dr Keoleian estimated using the USDA's Loss Adjusted Food Availability dataset as a proxy for per capita food consumption in the United States.

Researchers at the University of Michigan say following dietary guidelines (stock image shown) could increase greenhouse gas emissions. They say certain guidelines do not have environmental impacts in mind. In the study they found the USDA 2010 Dietary Guidelines would increase emissions by as much as 12 per cent

While a drop in meat consumption would help cut diet-related greenhouse gas emissions, increased use of dairy products - and to a lesser extent seafood, fruits and vegetables - would have the opposite effect, increasing diet-related emissions, according to the researchers.

In the US in 2010, food production was responsible for about eight per cent of the nation's greenhouse gas emissions.

In general, animal-based foods are responsible for more greenhouse gas emissions per pound than plant-based foods.

The production of both beef cattle and dairy cows is tied to especially high levels of greenhouse gas emissions.

For starters, cows don't efficiently convert plant-based feed into muscle or milk, so they must eat lots of feed.

Growing that feed often involves the use of fertilisers and other substances manufactured through energy-intensive processes. And then there's also the fuel used by farm equipment.

In addition, cows burp lots of methane, and their manure also releases this potent greenhouse gas.

In general, animal-based foods are responsible for more greenhouse gas emissions per pound than plant-based foods. The production of both beef cattle and dairy cows (stock image shown) is tied to especially high levels of greenhouse gas emissions, say the researchers

Greenhouse gas emissions associated with producing the US diet are dominated by the meats category, according to Dr Heller and Dr Keoleian.

While beef accounts for only four per cent by weight of the food available, it contributes 36 per cent of the associated greenhouse gases, they conclude.

The researchers found that a switch to diets that don't contain animal products would lead to the biggest reductions in this country's diet-related greenhouse emissions.

But Dr Heller said he's not arguing that everyone should go vegan, and he believes that animals need to be part of a sustainable agricultural system.

However, reduced consumption would have both health and environmental benefits.

In their paper, Dr Heller and Dr Keoleian also looked at wasted food and how it contributes to US greenhouse gas emissions.

They concluded that annual emissions tied to uneaten food are equivalent to adding 33 million passenger vehicles to the nation's roads.