The author responds to “Canada Food Guide’s focus on reducing saturated fat contradicts evidence”

I thank Drs. Bradshaw and Loffelmann1 for their contribution to the discussion of plant versus animal product–based nutrition and response to the commentary in CMAJ.2

They suggested that the National Academies of Sciences, Engineering and Medicine in the United States have criticized the Dietary Guidelines Advisory committee (DGAC) and Dietary Guidelines for Americans (DGA) for a lack of sound science in recommending a low-saturated–fat and more plant-based diet for Americans.3 I note that the academies stressed that the findings of their report “should not be considered as judgments about the quality of prior DGA or DGAC reports.”3 It is also worth noting that the submissions to the DGA were both for and against a shift to a more plant-based diet; however, on the issue of sustainability, most submissions supported its inclusion in the guidelines.3

These comments by the academies do not sound like criticism of the US guidelines as inferred.

Bradshaw and Loffelmann1 quoted the Prospective Urban Rural Epidemiology (PURE) study4 as supporting low-carbohydrate, high-meat diets. Certainly, the socioeconomic status of those on high-carbohydrate diets was low, and we know that socioeconomic status is a powerful driver of health outcomes that may be difficult to control for.4 However, perhaps more telling is a second article by the PURE investigators in the Lancet showing that consumption of legumes, fruit and vegetables (good sources of carbohydrates) are associated with overall longevity (reduced all-cause mortality).5 Perhaps these findings may be interpreted as indicating that fat may be better than bad carbohydrates, but that carbohydrates with a low glycemic index (eaten in increased amounts by vegetarians and vegans) have benefit.

Bradshaw and Loffelmann1 also cited a meta-analysis by Astrup and colleagues that milk consumption is not associated with cardiovascular disease and all-cause mortality.6 However, no benefits were shown for milk, and the authors of the meta-analysis stated that the background diet was not reported in half the studies they assessed and that elimination of bad foods (e.g., soft drinks or meat) by milk may have falsely inflated the apparent benefits for milk and masked some of its adverse effects.6 Overall, I do not see the lack of effect of milk on all-cause mortality as a strong reason for the continued promotion of milk.6

Children and adverse effects are always a cause for concern; in this instance, Bradshaw and Loffelmann1 cited a review (that is not systematic and certainly not a meta-analysis) by Cofnas.7 This review put together the possible adverse effects of soy intake and vegan and vegetarian diets on outcomes in pregnancy and childhood intellectual development in those not consuming meat. This review is of interest, but important studies, such as one by Andres, Badger and colleagues that used magnetic resonance imaging and followed children who had consumed soy formula in early life, were not cited.8 They found no persistent effects (including anatomic changes) after feeding with soy infant formula, despite the substantial phytoestrogen content in the soy formula.8 Most importantly, Cofnas’ stance against plant-based diets runs counter to the positions of the US Academy of Nutrition and Dietetics9 and the US Department of Agriculture,10 both of which state that wisely selected plant-based diets have no negative effects on children9 and are recommended for the general population,10 as Cofnas noted in his review

I continue to conclude that well-balanced, plant-based diets can be good for human health and, perhaps more importantly, may be essential for the survival of all life on this planet.