Peat is against yoghurt primarily for the lactic acid content that he considers a metabolic burden, but studies consistently show yoghurt consumption is associated with better health, even more so than other dairy products. One of the earliest written mentions of yogurt by Pliny the Elder specifically emphasises the "agreeable acidity" of yogurt (Yogurt - Wikipedia) produced by its lactic acid content. Why would something that is a metabolic burden produce an agreeable taste, is there more to lactic acid?
There is a ton of research showing that lactic acid has antibacterial properties, some show it can even potentiate the antibacterial properties of other agents (eg Lactic Acid Permeabilizes Gram-Negative Bacteria by Disrupting the Outer Membrane), could it be that consuming yogurt and other fermented foods are beneficial to human health by acting to clean the gut from bacterial overgrowth? Is it possible the negative effects some report from consuming yogurt is not due to the lactic acid directly but rather due to endotoxin being released by dying bacteria? If so one would expect the negative effects from yogurt consumption to be transient and followed by better health in the longterm, as the epidemiological studies suggest.
There is a ton of research showing that lactic acid has antibacterial properties, some show it can even potentiate the antibacterial properties of other agents (eg Lactic Acid Permeabilizes Gram-Negative Bacteria by Disrupting the Outer Membrane), could it be that consuming yogurt and other fermented foods are beneficial to human health by acting to clean the gut from bacterial overgrowth? Is it possible the negative effects some report from consuming yogurt is not due to the lactic acid directly but rather due to endotoxin being released by dying bacteria? If so one would expect the negative effects from yogurt consumption to be transient and followed by better health in the longterm, as the epidemiological studies suggest.