Eating used to be so simple. If you liked it and could afford it, down the hatch it went. Yum-yum, end of story.

But the days of carefree consumption of food, alas, are a thing of the past, especially for meat lovers.

If nonstop - and contradictory - pronouncements by doctors as to what you should or shouldn't ingest don't spoil your appetite, dire warnings about the ruinous impact of your favorite dish on the environment or the climate probably will.

The fact that a billion people in the world live in or close to the edge of hunger is also a sobering reminder that even basic needs should never be taken for granted.

So what's a gourmand to do?

For those who enjoy the luxury of choice, help has come in the form of what may be the most wide-ranging overview so far on how different foodstuffs - from lentils to lamb chops - impact the environment, the fight against global warming, and the human body.

A Meat Eater's Guide to Climate Change and Health is just that, a 90-page no-nonsense manual to help define a personal comfort zone between what your taste buds crave and what your conscience will allow them to experience.

Start with the rising threat of climate change, fuelled not just by gas and oil combustion but methane-belching animals and the long chain of production that brings their selected body parts to middle-class dinner tables the world over.

"Our assessment calculates the 'cradle-to-grave' carbon footprint of each food item based on greenhouse gas emissions generated before and after the food leaves the farm," said Kari Hamerschlag, a senior analyst at the non-profit Environmental Working Group in Washington DC.

The analysis, jointly conducted with the Portland, Oregon-based CleanMetrics Corporation, also includes the pesticides and fertilizers used to grow animal feed, the raising of livestock, and the processing, transportation and cooking that follows.

Even disposal of leftovers - a major source of emissions and pollution - is taken into account.

The same criteria are applied to various farmed fish, grains, dairy products and vegetables too. No surprise, meat is the prime offender across almost all categories considered.

But not all edible critters are equal, at least not when it comes to their harmful impact.

Pound-for-pound, lamb is the worst carbon polluter, generating nearly 40 kg of CO2-equivalent for every kilogram eaten. The next most carbon-intensive animal - also a cud-chewing ruminant - on the list is beef, with emissions of 27 kg for each kilogram consumed.

Looked at another way, eating a modest 110-gram slice of braised lamb shank is the equivalent of driving a mid-sized car for 21 km. The same amount of beef works out to just over half that distance.

"If your family of four skips steak once a week, it's like taking your car off the road for nearly three months," Hamerschlag said.

People in the United States eat more meat - exceeding Europeans by 60 percent - than most other developed nations, with 100 kg produced each year for every man, woman and child.

But burgeoning middle-class appetites in rapidly emerging economies are closing the gap, recent studies have shown.

In terms of health, the study reviews the well-known hazards of excess meat consumption, including heart disease, diabetes and obesity. It also highlights the widespread and controversial use of antibiotics for livestock and, in the United States, growth hormones.

The next culprit on the scale of climate and environmental impacts is cheese, mainly because of the large quantities of milk needed to produce it.

Runoff from waste into fresh water sources and even the ocean is especially problematic.

As is the fact that global consumption of all meats combined has soared, from about 70 million tons in 1960 to about 300 million tons today.