When countries design school-feeding programmes or calculate food import requirements, they base their decisions on standardised estimates of how many calories people need to lead active and healthy lives.
Experts, invited by the Food and Agriculture Organisation, the World Health Organisation and the United Nations University, met for the Expert Consultation on Energy in Human Nutrition, the first such consultation since 1981.
Their aim was to assess estimates, revise figures for certain groups and discuss a new concern in the developing world: obesity.
"There's been a long lag since the last consultation," says Eileen Kennedy, former Deputy Under-Secretary for Research, Education and Economics for the US Department of Agriculture and chair of the consultation. "The good news is that today we have better and more precise information." The recommendations from the consultation will be released in a report later this year.
In a recent statement the FAO highlighted the discovery that one of the most significant changes since the last consultation is the emergence of obesity in countries still struggling to end hunger.
A combination of increased income and the availability of more food, but not necessarily better food, is behind this change. So too is the fact that activity levels are decreasing in much of the developing world. In many cases, obesity occurs in the same household as hunger.
Experts at the consultation agreed that obesity needs urgent attention. They maintain that part of the solution is promoting physical activity since activity confers important health benefits and also burns calories.
A number of assumptions about lifestyle were also challenged at the consultation. It turns out that people in the developing world are becoming less active than they used to be. Increased automation in agriculture means farmers expend less energy to get the same work done. And as incomes rise, people are adopting a more sedentary lifestyle, for example travelling by motorized vehicle rather than by foot.
The rise in obesity also questions some basic assumptions about energy recommendations. For example the report from the last consultation had recommended providing additional food to undernourished children to allow them to catch up to normal weight. But at this consultation, experts from a number of developing countries pointed out a problem with this approach. "When the information was used to plan feeding programmes, it actually led to obesity in some cases," said Prakash Shetty, Chief of FAO's Nutrition Planning, Assessment and Evaluation Service.
On a positive note, participants did confirm the validity of most of the previous energy recommendations - which was reassuring after years of criticisms that the figures might be too high. But better data using new tools led them to revise energy requirements for certain groups. For instance, scientists discovered that children are less active than previously thought and as result, need fewer calories. By contrast, adolescents need more calories.
Specific recommendations for pregnant and breast-feeding women will also be revised. Energy requirements may decline in some cases since it turns out pregnant women are less active than previously thought. But instead of giving a single recommendation for how much weight gain leads to a healthy birth, a calculation will be made considering whether the mother is underweight or overweight.
And whereas the previous recommendations lumped everyone over 60 years of age in one group, the new guidelines will have sub-groups.
"There's a big difference in energy needs and expenditures for individuals between 60 and 75 years old and those who are 75 and over," said Irwin Rosenberg, Professor of Physiology, Medicine and Nutrition at Tufts University School of Medicine. People in their 60s and 70s may still be very active members of the household. But with increasing age people tend to exercise less while the body loses muscle mass - thus requiring fewer calories overall. Both factors are more pronounced in those over 75.
The FAO stressed that the new report will reflect all these changes.