As we all know by now, mobile phone use is skyrocketing.  In Columbia, for example, there are more mobile subscribers per 100 inhabitants than in the US (92 vs 87 as of 2008 data)! And in Africa, about 40% of the population owns a mobile phone –  from essentially zero ownership 10 years ago. 

There is a lot of talk these days about "mHealth", but there's another way that mobiles are affecting health: as a labor-saving device.

In rich countries, where most of us have the problem of "too much food and not enough exercise" the last thing we need is a way to burn even fewer calories, but in populations at the edge of malnutrition anything that saves labor saves calories.  Something that saves you from burning 1000 calories is nutritionally the same as giving you 1000 calories of food.

Well, for billions of people around the world, mobile phones do help people burn fewer calories simply by making it possible to communicate with other people over distance -- without having to burn calories walking, in most cases, to that other person.

Think, for example, of the calories a mother might expend in carrying her child to a clinic five or ten miles away. Those calories might exceed her daily caloric requirement – and she might arrive only to find that nurse was not even present that day, or that the clinic had no medications! Scarce calories wasted (not to mention the wasted time).

For that mother, the ability to call the clinic and find out that the health worker is not there, or that the clinic is closed or out of meds -- without having to make the trip -- could be the equivalent of getting an extra day’s supply of food!  

On a broader scale, consider Kenya, which now has roughly 16 million mobile phones. If we consider just the poorest 1 million mobile phone owners in the country, and we assume that each of those million poor people save at least 100 calories per week by calling instead of walking :

1 million people x 100 calories x 52 weeks = 5.2 billion calories saved per year

Five billion calories saved per year! That is the caloric equivalent of having the World Food Program distribute about 11 million high-energy biscuits in the country per year (but without the costs in shipping, fuel, insurance, and personnel).  And for each of those people it is as if they’ve been given an extra 5200 calories per food each year: two days worth.

Of course, these numbers are inexact, and the poorest of the poor probably don’t have a phone (yet). Regardless, the numbers serve to give us some idea of the tremendous unexpected effects occurring as mobile phone penetration increases: bad news for those of us struggling to keep our weights down, perhaps, but very good news for those with the opposite problem.