Dietary carbohydrate intake and mortality: reflections and reactions
Authors: Nina Teicholz
Journal: The Lancet Public Health (2018)

There are several problematic issues in the Article by Seidelmann and colleagues.1Seidelmann 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 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.1Seidelmann 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 Food was clearly underreported, as evidenced by a reported average energy intake of roughly 1500 kcal per day. Second, their results differ from many rigorous, randomised, controlled clinical trials that, taken together, concluded that carbohydrate restriction can reverse type 2 diabetes and improve most cardiovascular risk factors and that carbohydrate restriction is equal to or superior than any other diet for weight loss.2Halberg SJ McKenzie AL Williams PT et al.Effectiveness and safety of a novel care model for the management of type 2 diabetes at 1 year: an open-label, non-randomized, controlled study.Diabetes Ther. 2018; 9: 583-612Google Scholar, 3Johnston BC Kanters S Bandayrel K et al.Comparison of weight loss among named diet programs in overweight and obese adults: a meta-analysis.JAMA. 2014; 312: 923-933Crossref PubMed Scopus (384) Google Scholar, 4Santos FL Esteves SS da Costa Pereira A Yancy Jr, WS Nunes JP Systematic review and meta-analysis of clinical trials of the effects of low carbohydrate diets on cardiovascular risk factors.Obes Rev. 2012; 13: 1048-1066Crossref PubMed Scopus (194) Google Scholar The authors need to explain a mechanism by which such improvements in health could ultimately shorten lifespan. Third, the moderate-carbohydrate diet that Seidelmann and colleagues found to be optimal (at 50–55% of calorie intake) has, in fact, already been tested in clinical trials5Howard BV Horn LV Hsia J et al.Low-fat dietary pattern and risk of cardiovascular disease: the Women's Health Initiative randomized controlled dietary modification trial.JAMA. 2006; 295: 655-666Crossref PubMed Scopus (868) Google Scholar, 6Knopp RH Walden CE Retzlaff BM et al.Long-term cholesterol-lowering effects of 4 fat-restricted diets in hypercholesterolemic and combined hyperlipidemic men. The dietary alternatives study.JAMA. 1997; 278: 1509-1515Crossref PubMed Google Scholar, 7Walden CE Retzlaff BM Buck BL et al.Differential effect of national cholesterol education program (NCEP) step II diet on HDL cholesterol, its subfractions, and apoprotein AI levels in hypercholesterolemic women and men after 1 year: the beFIT Study.Arterioscler Thromb Vasc Biol. 2000; 20: 1580-1587Crossref PubMed Scopus (50) Google Scholar on more than 50 000 people; results of these previous trials showed that this moderate-carbohydrate diet had no benefit in combatting diabetes, obesity, heart disease, or any kind of cancer. Such a moderate-carbohydrate diet was found to cause high-density lipoprotein-cholesterol to decrease and the blood concentration of triglycerides to increase, which are both signs of worsening cardiovascular risk. The authors need to address the disparity between the findings from their observational study and those from the more rigorous clinical trial evidence. I report that I am the author of a book on this topic, The Big Fat Surprise. Dietary carbohydrate intake and mortality: reflections and reactionsI read Sara Seidelmann and colleagues study1 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. Full-Text PDF Open AccessDietary 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 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