You are not permitted to download, save or email this image. Visit image gallery to purchase the image.
Prof Mann said that aspects of the findings were "very confusing and misleading''.
"Processed meat has been repeatedly shown to be carcinogenic,'' he added in an interview.
Eating red meat had also long been linked with heart disease, and to the consumption of accompanying saturated fat.
The researchers, from Canada, Spain and Poland, reviewed studies on links between meat consumption and human health.
In controlled trials, they could not find a statistically significant association between meat consumption and the risk of heart disease, diabetes, or cancer.
Based on their reviews, a panel of 14 international specialists recommended that most adults should keep eating their present levels of red and processed meat - estimated at three to four times a week in North America and New Zealand.
The findings, arising from reviews and published in Annals of Internal Medicine, were "potentially unhelpful and could be misleading'', Prof Mann said.
"It's the headline message that's totally confusing,''he added.
He queried the "weak recommendations'', based on "low certainty'' evidence, arising from reviews by the researchers, that adults "continue current consumption of unprocessed red meat and processed meat''.
Most existing dietary guidelines recommend cutting down on these meats, but the review authors said the actual risk reductions are often trivial for people lowering their red or processed meat consumption by three servings per week, and any links between meat consumption and negative health effects are uncertain.
Based on these reviews, which include some Australian and New Zealand data, an accompanying guideline recommends most adults should continue to eat their current levels of red and processed meat, the researchers said, in a summary by the Science Media Centre.
Prof Mann, who is co-director of the university's Edgar Diabetes and Obesity Research Centre, were based on a majority decision of the 14-member panel.
He did not question the integrity, expertise and good intentions of the leadership team and panel, but he had some reservations about the "guidelines'' they had issued.
The panel's recommendations for red meat intake by individuals were not appreciably different from that made by other organisations, such as the World Cancer Research Fund, given that current consumption in many countries was about three to four portions per week.
The recommendations to limit intake of red meat, in terms of effects on human health, were mainly based on the relationship between red meat and colorectal cancer, he noted.
Prof Mann, who is also director of the Healthier Lives National Science Challenge, said the panel did not take into account "environmental and animal welfare issues'' in making their recommendations.
"Don't forget about sustainability,'' he said.
It was"irresponsible not to consider sustainability and planetary health"- a key, if not the major, determinant of the health of future generations - when developing nutrient and food-based dietary guidelines.
The authors had acknowledged the limitations of their approach, and the low quality of the evidence, but Prof Mann was "not persuaded that it is even appropriate to suggest on the basis of these data that red meat may have little or no effect on disease incidence and mortality''.
He noted that the reviewing group does not represent any national or international organisation or government.
Prof Mann, who is a member of the World Health Organisation Nutrition Guidance Advisory Group, said guidelines were generally issued by "authoritative bodies rather than self-selected groups''.
Guidelines were generally issued by authoritative bodies rather than self selected groups, he said.
Prof Nick Wilson, of the department of public health at Otago University's Wellington campus, said the new review findings lacked "a critical wider context'', given there was "an urgent need for a global shift to a more plant-based diets for planetary health reasons''.
Current patterns of meat consumption were "completely unsustainable and are damaging the climate, polluting waterways, and depleting water supplies''.
From the human health risk perspective, the new review findings were also "out of sync with other major reviews'', including a major review by the International Agency for Research on Cancer, involving more than 800 studies, on processed meat and red meat and increased risk of cancer.
Processed meat was also invariably high in salt, which was a proven risk factor for raised blood pressure and cardiovascular disease, he said.