In developing countries, higher waist circumference is positively tied to infant survival, which is the opposite situation from the West. A jungle horticulturalist diet is marginal to begin with* and then you add in pregnancy food taboos and parasites, and it's understandable why this is the case. Extra body fat is a buffer.
These also could be women who have just given birth. Either way, anthropologist Steven Gaulin says that women tend to gain weight around the middle as they either age or have children because of the fact that it helps support larger babies, who are more likely to survive. A woman who has had many children already has a stretched pelvis and can handle it. And older women who has never given birth before...well, natural selection is figuring she isn't going to have many children and the ones she has better survive, even if it's at the cost of her life.
From what I know, the health of infants in Papua New Guinea is a little better than the Hadza, which another person mentioned. The Hadza are too thin and their health suffers for it. As far as I'm concerned it's an indication that the Hadza and other "bushman" tribes are adapted to an environment that was once more plentiful. The Melanesians have been living in their locality for a very very long time and are very much genetically distinct. Sexual selection could also be a factor, as interviews with Melanesians typically confirm that men prefer women with a higher WHR than the West or Asian, and that women desire to have "fat arms."
Then the pattern is that after menopause, a woman in these cultures (and in our culture until very recently) gets thinner and thinner, which is sometimes referred to as "wasting." I understand why Western women take hormonal replacement to avoid the negative effects of this, but it often means they keep the weight.
Either way, none of these women are obese. In America, many people are so overweight that it affects their mobility. They would not be able to use that boat the first woman is in.
*did anyone see the human planet episode in Papua where they are hunting bats and talking about how little meat they get? Meat hunger is quite common in the jungle and it's debatable whether the jungle is really any more of an optimal environment than a modern European city. Also, if you want to see how much better coastal/island Melanesians look, do a search for "Trobriand" on Flickr.