With such serious weight issues also comes the threat of deadly non-communicable diseases such as heart attacks and diabetes.
The crisis has been largely attributed to traditional attitudes, where women have long been expected to stay at home with the family, instead of getting active and taking part in sports.
But times are changing.
Presenter: Catherine Graue
Speakers: Mo'onia Gerrard, former Australian netballer, Katalin Baranyi, Tongan Netball Association
Sound from promotional video: You can, I can, we can!
GRAUE: That's the message from Mo'onia Gerrard, a former Australian netballer...
She's slim, she's super fit and she's half Tongan.
She's in the country this week, recruited to help promote healthy lifestyles and netball amongst Tongan women, including running workshops with coaches and umpires.
GERRARD: I was just trying to engage in with some of the skills that I've learnt coming through the ranks in netball and also as a coach now, and try to deliver what kind of skills that they could probably take into their teams that they coach, and also within their little village that they live in. But I guess within the Tongan structure, the Tongan teenage structure, we want to build the coaches here within Tonga, so then they get some more development, they're confident at what they're delivering so then we can expand and have more umpires and more coaches, which then means more development officers to reach out to the communities that we can't actually reach out, because of the limited resources that we have.
GRAUE: The project, which is a partnership between the governments of Australia and Tonga, as well as the netball associations of those countries, is now into its third year.
But it's already having tangible impacts.
Katalin Baranyi is the National Operations Manger with Tonga's Netball Association.
BARANYI: So that more teams are coming up and more people are more focussed and using netball as healthy living to prevent all the diseases like NCDs, because we as you know have the highest obesity in the Pacific, in Tonga in general, and we try to go back to the ideal Tongan figure since the 1970s, early 70s.
GERRARD: We see more women or just more people in general walking early in the morning to do their daily exercise. Groups of women come together to do their walks that they have that week. So you see more girls and people in general just going out walking or doing some activity early in the morning and late in the afternoon. So from what I had experienced in the previous years that I've been here - outside of this program - you hardly saw any of that. For me running down the road was a bit rare and silly, "how dare you" kind of thing. But for me, seeing those girls and the people here in Tonga embrace that healthy lifestyle it's definitely growing.
GRAUE: But changing attitudes hasn't been without difficulty, as Katalin Baranyi explains
BARANYI: There are some areas it's really changed, sometimes you go to the rural areas it's really hard because of traditional like women stay home. Well we're trying to empower these women to come out and play, come out with her daughters and play together and come as a team, come as a community. It's changed slowly but we've seen how it's changed within the villages, and we saw the numbers of the participation of the last tournament.
GRAUE: While in Tonga, Mo'onia's also working with a development squad - which it's hoped, will become Tonga's National Netball team.
GERRARD: I have to admit they're quite raw in the way that they play their netball because the development hasn't been there. But if I was to go by the feedback of other officers that have gone to the other islands, sister islands like the Samoans, the Fijians, the Cook Islands, the feedback has come back saying that our younger girls, the generation that we have coming through the ranks now are more highly skilled and fitter and I guess their physique is not as bigger as much as those other countries.
GRAUE: After many years without a national team, the Tongan Netball Association is hoping the team will be able to compete at the 2019 Pacific Games, which Tonga is hosting.
And they're aiming high.
Katalin Baranyi again:
BARANYI: Where there's a will there's a way. I'm sure we are ready and we're ready by 2019. There's about four or five years from now, so we'll be ready and we're just trying to motivate and get people that can carry on exercising and looking forward, there's a target there for us and we just have to go through whatever steps it may take us to achieve and reach 2019. And hopefully we take the gold medal here while the sport is in Tonga though.