As thousands of scientists, activists and policymakers gather in Rio de Janeiro for the 26th International Aids Conference next week, much of the discussion will focus on protecting decades of progress against HIV in the face of devastating global funding cuts.

But one of the most important lessons from the HIV response reaches far beyond HIV itself.

South Africa has already lived through one epidemic in which stigma kept people away from effective treatment. We shouldn't repeat those mistakes as obesity emerges as one of the country's biggest health challenges.

A woman at an HIV research site in Yeoville, Johannesburg, understood this dilemma long before most people did.

In 2019, she asked her doctor a question through tears: "Why can't I stop gaining weight?"

Her HIV treatment was working exactly as it should. The three-drug regimen had suppressed the virus to undetectable levels and restored her health.

She kept replacing her wardrobe with bigger clothes. Her doctors encouraged her to eat less and exercise more, but nothing seemed to help.

Her story captures a challenge South Africa is only beginning to confront. As obesity rates rise and demand for exorbitantly-priced weight-loss medicines grows, the public is increasingly turning to unsafe and illegal copies of registered products sold on social media while many healthcare workers continue to frame obesity as a failure of willpower rather than a chronic disease that often requires medical treatment.

Weight loss injections, such as "Reta", which is still in trial, are now widely marketed on WhatsApp, Instagram and TikTok, often at prices that make them attractive to people who have few safe alternatives. Desperation, fuelled by stigma and a lack of access to evidence-based care, creates a market in which false hope can flourish.

**A new stigma built on the same assumptions **

South Africans have seen this pattern before.

For years, dramatic weight loss was widely regarded as a tell-tale sign of HIV. Many people delayed testing or treatment because they feared the judgment that came with an HIV diagnosis. Political denialism then deepened the crisis, costing countless lives by delaying access to medicines that could have prevented illness and death.

Science eventually prevailed but it was activism that transformed South Africa's response. HIV stopped being treated as a moral failure and came to be recognised as a medical condition that demanded rights, evidence-based care and access to treatment.

Today, South Africa faces a different form of stigma but one built on remarkably similar assumptions.

Weight stigma rests on a set of ugly assumptions: that people in larger bodies lack self-control, eat too much and the "wrong" foods, and are too lazy to exercise.

Research now shows that obesity, like high blood pressure or raised blood sugar, is a progressive disease that often requires treatment and reflects genes, environment and a changing food supply — not simply bad choices.

Society and much of medicine has not caught up.

Higher-weight people are still imagined as greedy or weak, their illness treated as a deserved consequence rather than a condition worthy of care. This moral framing turns body size into a character test: thin people's illness is met with concern, while larger people are met with lectures and jokes — including from healthcare workers.

**How HIV and obesity overlap **

South Africa's HIV and obesity epidemics overlap in ways that should worry anyone working in health.

Newer antiretroviral regimens (ARVs) are linked to greater weight gain than older treatments, with the largest increases seen in women and Black patients. Some of this is the body's "return to health" after HIV is controlled; some appears to be a direct weight-gain effect of the drugs themselves, since some older ARVs actually caused weight loss.

For many people, the result is a shift from one stigma to another: someone who once feared being seen as too thin now feels judged for being "too big", carrying the double burden of a hidden HIV status and highly visible body-size judgment.

At the same time, South Africa has seen a staggering rise in obesity among people without HIV, driven by food environments dominated by cheap ultra-processed products, poverty, stress and ageing.

The two trends are not separate; they share many of the same structural drivers.

This is where South Africa's HIV history offers a warning. In the early 2000s, influential global health voices argued that HIV prevention in Africa was far more cost-effective than treatment. A widely cited 2002 analysis in The Lancet framed prevention as much more cost-effective than antiretroviral therapy in sub-Saharan Africa. In practice, that kind of thinking helped normalise the idea that poor people should wait for treatment while prevention efforts were strengthened — that, in effect, the failures of prevention should be left to die.

South Africa knows how destructive that logic became. Access to ARVs expanded not because the argument faded away, but because activists, clinicians, researchers and communities forced treatment access into the centre of public life.

**Why prevention and treatment aren’t rivals **

Today, the debate around obesity medicines sounds eerily familiar.

The arrival of GLP-1 receptor agonists — drugs that help people feel fuller for longer and eat less — has caused real excitement. This group includes, amongst others, semaglutide, sold as Ozempic and Wegovy, and tirzepatide, sold as Mounjaro and Zepbound. For some people, these medicines can lead to major, life-changing weight loss.

But it has also triggered a backlash: warnings that obesity is being over-medicalised, that people are looking for an easy fix and will abandon healthy eating and exercise, that treatment must not distract from prevention and that it will bankrupt medical aids and the country.

In HIV, we heard the same arguments: that treatment access played into the hands of "Big Pharma", that people would abandon condoms for reckless sex, that the country could not afford the medicines, and that we could not "treat our way out of the epidemic".

Two decades on, it would seem quaint if those commentators hadn't been so disastrously wrong for millions of people.

Of course, prevention matters. No medication will fix ultraprocessed food markets on its own, make healthy food affordable, make neighbourhoods safer, raise wages, or fix school food environments.

But the lesson from HIV is not that prevention and treatment are rivals — it's that you need to do both at once. Withholding effective treatment from people who need it now, especially poorer people, causes avoidable harm. The government needs to take control of both sides of this: strong regulation and enforcement to address the upstream causes of weight gain, alongside better medical care for people already living with obesity.

That lesson is especially important for people living with HIV.

How HIV's lessons can help fight obesity stigma

In South Africa, many of those most affected by ART-associated weight gain are women using public sector services. Yet medicines that could help people manage that weight gain are not available through South Africa's public health system, where they receive their HIV treatment.

This is a cruel irony: lifesaving ARVs are available, but support for one of its commonest side effects is not. Patients are left alone with a problem that is medical, social and deeply personal.

There is another lesson South Africa should borrow from the HIV response: let affected communities lead.

HIV activism changed the country because people living with HIV, and the organisations that stood with them, refused to be treated as passive recipients of policy. They demanded treatment, challenged language, reshaped public debate and exposed the politics of drug pricing.

By contrast, most major anti-stigma work on obesity, around the world, has been led by researchers and professional societies, not by a broad, visible, community-led movement. The vested interests that dominate the food and weight-loss industry are every bit as powerful as the pharmaceutical industry, far less regulated, and have successfully lobbied the government at multiple levels. People speaking up together is needed to fight everything from attacks on the sugar tax to fast-food companies sponsoring school furniture.

Today, South Africa stands at a fork in the road.

On one side is an unregulated market of social-media weight-loss drugs, where people who are desperate and ashamed take real risks because the health system has given them little else. On the other is a set of effective, well-studied obesity medicines — such as GLP-1 agonists — largely reserved for people who can afford them.

**What SA should do next **

Doing better would mean three things.

First, regulators need to clamp down on illegal and unsafe products, while giving the public clear guidance on which treatments actually work.

Second, the health department and medical aids should provide access to GLP-1s and other obesity care within HIV services, for those at highest risk — alongside, not instead of, stronger food and prevention policies.

Third, training for HIV nurses and doctors must treat weight stigma as a clinical harm, so that conversations about body size become kinder, more honest and more effective.

Civil society needs to start demanding the kind of systems-level change that made mass delivery of HIV treatment possible in South Africa.

The new obesity medicines are every bit as transformational as antiretrovirals were, and may have benefits reaching well beyond weight loss, into diabetes and other chronic diseases. But like the early wave of antiretrovirals, they are extremely expensive, have side effects that require real counselling and community support, and will have to be delivered to millions of people through primary care clinics, by nurses.

Most of all, we need a government committed to doing this: one that keeps fast-food companies out of schools, and has a properly funded plan to fix a food system that currently leaves people with no real choice but an unhealthy one.

HIV activism taught South Africa that stigma kills and treatment saves lives. As delegates in Rio spend this coming week trying to rethink, rebuild and rise for the next phase of the HIV response, they'd do well to apply the same lesson to obesity — before we replay the same mistakes on a new group of people whose bodies have already been judged enough.

Francois Venter heads up Ezintsha at Wits University; Simiso Sokhela is the clinical director at Ezintsha; Nzama Mbalati is the CEO of the Healthy Living Alliance, Heala, and Yvette Raphael is the co-founder and co-director of Advocacy for Prevention of HIV and Aids (Apha).