Blood-cancer patients who ate more sugar on antibiotics lost more gut microbiome diversity

The 24 per cent is a relative number. It measures how much larger the antibiotic-linked fall in diversity was for each extra 100 grams of high-sugar food or drink eaten in the 48 hours before a stool sample ^[7]. A hundred grams is about one large milkshake ^[7]. The underlying fall varied from person to person ^[7]. The New Scientist report does not give its size, so the absolute diversity lost per milkshake cannot be worked out from the published account.

The exposure records are what make the study unusual. The tray logs come to more than 250 items per patient on average ^[1], collected from 12 days before transplant to 49 days after ^[4]. New Scientist says that level of detail is rarely possible in nutrition research ^[5]. "Suppose a patient ate half a lasagna. We know the recipe and the standard serving size and the nutritional information of each ingredient," Peled said ^[6]. "I think this is the closest anyone has ever come to precisely recording everything that goes in and linking it to what comes out." ^[6]

Precise records still produce an association. Patients who ate more sugary food may have differed in other ways that affect the gut, and a correlation across meal logs cannot exclude that. The mouse work adds a comparison the ward could not: the same sugary diet with and without the antibiotic. Mice on high sugar alone kept their bacterial diversity ^[12]. With biapenem added, the Enterococcus count roughly doubled again between day three and day six ^[2]. A commercial fruit smoothie high in fructose produced similar effects in mice, Peled said ^[13].

Jonas Schluter of NYU Langone Health, a member of the team, said antibiotics leave "last man standing" strains that are not necessarily the most beneficial ^[9]. "They have survived the assault and then we are feeding them with rocket fuel," he said ^[9]. Nicola Segata at the University of Trento said, "It makes sense that potential pathogens are boosted by sugar." ^[10] In his account, sugar can favour pathogens that cannot break down fibre, while the beneficial bacteria competing with them go without the fibre they need to recover ^[10].

The case for diet as protection rests on two further steps. Greater gut diversity has been linked to better survival in people with cancer ^[15], and that link is also a correlation. The reported work does not include a trial that assigned patients a low-sugar diet and followed what happened. Peled called limiting sugar "very feasible, likely to be very low toxicity" ^[17] and extended the idea past the hospital. "Many of us are motivated to find ways to protect the microbiome when we or our children are prescribed antibiotics. Limiting the intake of sugary foods offers a potential way to do that," he said ^[16].

I think the ward case is the strong one. These patients had their immune systems knocked out by chemotherapy and spent weeks in hospital, each taking at least one antibiotic ^[2]. Healthy adults and children on a short outpatient course were not in the study ^[1]. For them, the evidence here is a mouse result plus an extrapolation from transplant wards.