The tech behemoth's proposal to acquire the wearables firm for about $2.1 billion is being scrutinised by the Australian Competition and Consumer Commission and the European Commission.

Google says the deal is about devices, not data, and has promised not to use fitness and wellness data of 28 million Fitbit users for ads.

But a group of economists, including two from Melbourne, are concerned sensitive health data held by Fitbit be added to users' personal profiles maintained by Google.

Those profiles already contain data from services such as Gmail, Maps and online searches.

Google could then infer healthcare information about non-Fit users, based on their similarities with Fitbit users, Professor Chongwoo Choe said.

"This is something that Apple, Samsung and other companies (in the wearables market) don't have - the scale of data that Google has from other services," the director of Monash University's Centre for Global Business told AAP.

He said people may think that because they weren't using Fitbit, the acquisition didn't matter.

"But Google can infer fairly large amounts of information," Prof Choe said.

"It should make people who don't use Fitbit wary as well because they are not immune."

Prof Choe, his colleague Associate Professor Zhijun Chen and 15 other global economists in September told the European Commission the deal would monetise health data and harm consumers.

Google's bid for Fitbit is consistent with its strategy to expand into healthcare, life sciences and insurance, Prof Chen said.

Connecting Fitbit data with user data from Google's Cloud Healthcare API would allow the tech giant to build a more comprehensive patient profile and offer more personalised health care.

"The Fitbit merger provides the chance for the European Commission and the ACCC to remain a frontrunner in the enforcement and guidance of merger policy in the digital era," Associate Professor Chen said.

Prof Choe said academics and policymakers all too often lamented a failure to intervene more decisively.

"Blocking the merger doesn't solve all problems related to health data, but it avoids amplifying already existing problems," he said.

Google said it worked hard to protect users' information and put them in control.

It was buying Fitbit to help its hardware efforts, where the business model was primarily about selling devices and services, not advertising, a spokesman said.

"This deal is about devices, not data," he told AAP in a statement.

"The wearables space is highly crowded, and we believe the combination of Google and Fitbit's hardware efforts will increase competition in the sector, benefiting consumers and making the next generation of devices better and more affordable.

"We continue to work with the regulators to answer their questions."

The ACCC has previously raised concern over the aggregation of data and the potential for Google to change how it approaches rival wearables' use of Google Maps and other services.

The results of its year-long inquiry are due to be announced on December 9 - ahead of the European Commission's decision on January 8.

"We continue to engage with the European Commission and competition authorities in other jurisdictions," an ACCC spokesman told AAP in a statement.

Australian Associated Press