Dietary carbohydrate intake and mortality: reflections and reactions
Authors: Jocelyn L Tan-Shalaby
Journal: The Lancet Public Health (2018)

I read Sara Seidelmann and colleagues study1Seidelmann SB Claggett B Cheng S et al.Dietary carbohydrate intake and mortality: a prospective cohort study and meta-analysis.Lancet Public Health. 2018; 3: e419-e428Summary Full Text Full Text PDF PubMed Scopus (354) Google Scholar with interest, and there are several shortcomings that deserve attention. Although, the authors appropriately acknowledge the limitations of data collection by questionnaire, in their study, participants were expected to recall their food intake over 25 years, in detail, over two sessions. Another important issue is that participants in the lowest carbohydrate quintile consumed a daily mean of 1558 kcal, 37% of which was from carbohydrates. This grouping contrasts with the established energy intakes from carbohydrate of the classic ketogenic (in which carbohydrates comprise about 5% of calorie intake) and the modified Atkins diets (about 10%). The food items listed under the plant-based diet also included items that are usually highly restricted in modern low-carbohydrate diets (such as peanut butter, bread, chocolate, and soft drinks). The authors state that low-carbohydrate diets with “increased animal protein and fat consumption have been hypothesised to stimulate inflammatory pathways, biological ageing, and oxidative stress”. On the contrary, emerging evidence2Kallens V Tobar N Molina J et al.Glucose promotes a pro-oxidant and pro-inflammatory stromal microenvironment which favors motile properties in breast tumor cells.J Cell Biochem. 2017; 118: 994-1002Crossref Scopus (11) Google Scholar, 3Martuscello RT Vedam-Mai V McCarthy DJ et al.A supplemented high-fat low-carbohydrate diet for the treatment of glioblastoma.Clin Cancer Res. 2016; 22: 2482-2495Crossref PubMed Scopus (63) Google Scholar, 4Schwartz K Chang HT Nikolai M et al.Treatment of glioma patients with ketogenic diets: report of two cases treated with an IRB-approved energy-restricted ketogenic diet protocol and review of the literature.Cancer Metab. 2015; 3: 3Crossref PubMed Google Scholar shows that low-carbohydrate diets do exactly the opposite; these diets are shown to decrease inflammation, reduce oxidative stress, mitigate tumour signalling pathways, delay ageing, and slow down cancer growth and proliferation. Preclinical studies5Alderman JM Flurkey K Brooks NL et al.Neuroendocrine inhibition of glucose production and resistance to cancer in dwarf mice.Exp Gerontol. 2009; 44: 26-33Crossref PubMed Scopus (34) Google Scholar of low glucose availability in cancer suggest that the lifespans of patients with cancer could increase when these people are given low-carbohydrate diets. In at least one study6Tan-Shalaby JL Carrick J Edinger K et al.Modified Atkins diet in advanced malignancies—final results of a safety and feasibility trial within the Veterans Affairs Pittsburgh Healthcare System.Nutr Metab. 2016; 13: 52Crossref Scopus (51) Google Scholar in humans, a low-carbohydrate diet was well tolerated in patients with cancer. Current low-carbohydrate diets were not correctly represented in the study by Seidelmann and colleagues. Further investigation should be encouraged before making broad claims about possible deleterious effects. I declare no competing interests. Dietary carbohydrate intake and mortality: a prospective cohort study and meta-analysisBoth high and low percentages of carbohydrate diets were associated with increased mortality, with minimal risk observed at 50–55% carbohydrate intake. Low carbohydrate dietary patterns favouring animal-derived protein and fat sources, from sources such as lamb, beef, pork, and chicken, were associated with higher mortality, whereas those that favoured plant-derived protein and fat intake, from sources such as vegetables, nuts, peanut butter, and whole-grain breads, were associated with lower mortality, suggesting that the source of food notably modifies the association between carbohydrate intake and mortality. Full-Text PDF Open AccessHigh ambitions for health equity in the AmericasOn Oct 1, 2019, the Pan American Health Organization (PAHO) published Just Societies: Health Equity and Dignified Lives, the report of the Commission on Equity and Health Inequalities in the Americas—a Commission established by PAHO , chaired by Sir Michael Marmot, and tasked to analyse the effect of drivers influencing health, while proposing actions to address health inequalities in the region. Full-Text PDF Open AccessDietary carbohydrate intake and mortality: reflections and reactionsEven if the Food Frequency Questionnaire had been robust and accurately reflective of what people had eaten during the whole 25-year study, a mean calorie intake of 1560–1660 kcal per day had been explained, and people had been allocated correctly to groups that reflected their actual carbohydrate consumption after a health diagnosis. Full-Text PDF Open AccessDietary carbohydrate intake and mortality: reflections and reactionsThe Article by Sara Seidelmann and colleagues1 presents the analysis from the Atherosclerosis Risk in Communities study of adults aged 45–64 years over a median duration of 25 years, at six timepoints. The mean caloric intake by each adult was 1558–1655 kcal per day. I have several issues with this study. First, this analysis seems to ignore the fact that, after 25 years, participants are aged 70–89 years, which is older than the 2016 estimate of life expectancy by the US Centers for Disease Control and Prevention: 78·6 years. Full-Text PDF Open AccessDietary carbohydrate intake and mortality: reflections and reactionsThere are several problematic issues in the Article by Seidelmann and colleagues.1 First, the quality of the dietary data is weak, since they are based only on two samples. The food frequency questionnaire that they used appears not to have been independently validated, and it contained only 66 questions and excluded several popular items, such as pizza.1 Food was clearly underreported, as evidenced by a reported average energy intake of roughly 1500 kcal per day. Full-Text PDF Open AccessDietary carbohydrate intake and mortality: reflections and reactionsIn their Article in The Lancet Public Health (September 2018), Sara Seidelmann and colleagues1 use data from a long-term prospective cohort study and do a meta-analysis of other related cohorts to assess the association between carbohydrate intake and mortality. Our main problem with this Article1 was regarding the confounders that are related to an individual's consumption of carbohydrates and to that individual's associated mortality. Some of these confounders were included as control variables, but since it is impossible to account for all possible confounders, some confounders necessarily went unobserved. Full-Text PDF Open AccessDietary carbohydrate intake and mortality: reflections and reactions – Authors' replyWe appreciate the interest in our work. We found that in long-term observational studies, low carbohydrate dietary intake (<40% of total energy from carbohydrates) was associated with higher mortality when animal-based fat and protein were substituted for carbohydrate.1 However, when plant-based sources of fat and protein such as whole grains, legumes, and nuts are incorporated into low carbohydrate diets, they were associated with lower mortality. We fully acknowledge the limitations of observational studies, while recognising the difficulties associated with long-term randomised trials in the area. Full-Text PDF Open Access