Health Minister David Clark has added one of New Zealand's most vocal advocates for a sugar tax to his office.

Former Dental Association spokesman Dr Rob Beaglehole is working in Clark's office as an adviser.

His appointment comes as pressure grows on the Government to slap a tax on sugary products, with two DHBs calling for sugary drinks to be made more expensive.

Beaglehole - dubbed the "anti-sugar man" in one media profile - has been a long-standing advocate of such a measure and was the dental officer of health for Nelson-Marlborough DHB.

His Twitter profile features a photo of soft drink bottles with Coca-Cola style labels: Tooth Decay, Cancer, Diabetes. As recently as last month he shared an article outlining a push by the NZ Dental Association to have cigarette-style graphic image warnings put on fizzy drink packaging.

Debate on a sugary drinks tax stepped up this week after the Herald revealed Capital & Coast and Hutt Valley DHBs had written to Clark, asking him to urgently put a tax on sugary drinks.

"For the first time in history, NZ children could live shorter lives than their parents as a result of excess weight and obesity," Andrew Blair, chair of both Capital & Coast and Hutt Valley DHBs, told Clark in both letters.

In response, Clark said there were no "immediate plans" for a tax on sugary foods or drinks, citing the Government's pledge to not introduce new taxes in the first term.

Instead, the Government has told the food and drink industry it expects less sugar in processed products. An overhaul of food and drink labelling is also being looked at.

Acting Prime Minister Winston Peters has rejected the call by the DHBs, telling Breakfast this week that "people are capable of looking after their own lives".

A Ministry of Health-commissioned report delivered in October 2017 concluded evidence for a sugar tax was inconclusive. Think-tank the New Zealand Initiative and other opponents of a tax argue studies relied upon by tax advocates vastly overestimate how much taxes would reduce consumption.

Sir Peter Gluckman, until recently the Prime Minister's Chief Science Advisor, told RNZ last month that the evidence for a sugar tax in countries like New Zealand had become much stronger in recent years. A report to Prime Minister Jacinda Ardern had outlined that change.

The NZ Beverage Council, which represents manufacturers, maintains evidence from overseas showed sugar taxes weren't effective.

"A sugar tax on sugar-sweetened beverages in Mexico has been shown to have had no impact on the caloric intake of the Mexican population and a sugar tax in Berkley actually resulted in the number of calories consumed by the population to increase as people substituted taxed soft drinks for non-taxed products with higher calories such as milk shakes, fruit juice and smoothies," a spokesman said.