Re: Implausible results in human nutrition research
We read with great interest Dr. Ioannidis’s paper on “Implausible results in human nutrition research: Definitive solutions won’t come from another million observational papers or small randomized trials” (1). While we can appreciate his editorial on the subject, this general discussion on the strengths and limitations of observational and experimental studies is not unique to nutrition and is commonplace in textbooks on epidemiological methods dating back to MacMahon and Pugh’s first text on the subject in 1970 (2). Strong commentary on the limitations of epidemiology in the study of nutrition can be traced back to Taubes’ article in Science in 1995 (3). A thorough rehashing of his arguments goes beyond the scope of this response, but in all areas of epidemiology (and other areas of scientific study), false positive and false negative results inevitably occur, and many studies lack replication. We discuss some of the main points below.
Dr. Ioannidis’s comment that “Many findings are entirely implausible” is not helpful as implausible finding occur by chance or other reasons in almost all areas of science, and conclusions should not be based on a single finding but rather the plausibility given all available evidence and on replication (1). In nutritional research, we usually evaluate the evidence from animal/mechanistic experiments, biological/metabolic findings, and epidemiological/intervention studies together to reach conclusions (4). No single study should stand on its own, especially now that decades of nutritional research are available. Similarly, no single editorial should completely dismiss the great value the last 50 years of research has provided. Dr. Ioannidis selectively picked a few estimates from the vast amount of nutrition literature without any context. More importantly, he did not include the 95% confidence intervals surrounding those estimates. The 95% CIs can provide important information on both certainty and uncertainty of the point estimates (5). In evidence-based nutrition, meta-analyses and systematic reviews instead of findings from a single study are used to develop recommendations or guidelines. Therefore, consistency and replications of the findings across different populations are extremely important.
If we use dietary fat and heart disease as a first example, the weak and inconsistent results mainly derive from early studies, which were not designed to investigate the fat-CHD association. However, they should not be interpreted as providing strong negative evidence (6). The limitations in early studies include small sample size; use of a single 24-hour recall for dietary assessment; lack of updated dietary measurement during follow-up; and no adjustment for total energy intake or other dietary factors. More recent large prospective cohort studies have addressed these limitations. Results from high quality observational studies correspond well with randomized controlled trials (Table 1). Interestingly, in a publication from 2005, Dr. Ioannidis made the similarly dramatic claim that “Most biomedical research findings are false for most research designs and for most fields” (7). Goodman and Greenland (and others) have provided detailed responses to this claim and identified the logical flaws of Dr. Ioannidis’ assertion (8-13).
Dr. Ioannidis concluded that in future we would need randomized controlled trials (RCTs) 10 times the sample size of the Prevención con Dieta Mediterránea (PREDIMED) study (1). Interestingly, the majority of nutrition trials, even the size of PREDIMED, would not have been proposed or conducted had there not been very compelling evidence of the benefits of the Mediterranean diet, olive oil, and nuts from short term trials with intermediate endpoint and observational studies with coronary heart disease - the exact studies Dr. Ioannidis argues against performing. Does Dr. Ioannidis suggest that we conduct randomized trials 10 times the size of PREDIMED based on no more than simple conjuring of hypothetical biological pathways connecting nutrition with long term health?
Contrary to common beliefs, RCTs are not immune to confounding and serious bias even if they are large, and they can provide seriously misleading answers (14). For example, RCT's of smoking cessation showed no benefit on mortality (15), very low birth weight, neonatal death or perinatal mortality (16). Also, studies such as the Women’s Health Initiative, with a $400 million arm to test the benefits of a very low fat diet, failed to test the fat hypothesis due to low compliance with the dietary intervention (17). The earlier Multiple Risk Factor Intervention Trial (MRFIT) also failed to test its original hypothesis due to poor adherence and found no significant effect of an intervention combining diet, smoking cessation and hypertension treatment on coronary disease (18). These issues will not simply disappear by increasing sample size and they will worsen with longer follow-up(14). Randomized trials are randomized and free of confounding only at baseline, and their interpretation is complicated by attrition and non-compliance that is subject to confounding and selection bias - the same issues we are concerned about in observational studies.
Finally, Dr. Ioannidis comment that “Definitive solutions won’t come from another million observational papers or small randomized trials” (1) over simplifies the conduct of nutrition research and shows a deeper misunderstanding of the field. Because of the complex nature of our field, conclusions need to be based on the broader totality of evidence from human observational and clinical studies. In the past decades, cardiovascular mortality has decreased dramatically in Finland, US, and other developed countries, and more than half of the decline is attributable to improvement in diet and lifestyle factors. The landmark North Karelia study (44), the Seven Countries Study (45), the Framingham Heart study (46), the Minnesota Heart Health Program (47), and many other studies have shown that his claim of implausible nutrition finding does not hold water. A recent example would be trans fat. Well conducted long term observational studies and small randomized trials provided consistent and convincing evidence of the adverse effects of trans fat on lipid levels, inflammation, endothelial dysfunction, and significantly increased risk of coronary heart disease (48, 49). Despite the lack of large, long-term trials (48, 49) important changes were made to nutritional labels and policies across the globe, and food companies have removed up to 80% of trans fat in foods in the US. This clear public health advance was made with just the evidence that Dr. Ioannidis scorned; millions of premature deaths will be prevented that would not have been had we waited to conduct a mega-trial of trans fat to prove harm, and which could easily provide misleading results if it had the same fate as the WHI or MRFIT trials.
Reference:
1. Ioannidis JP. Implausible results in human nutrition research. BMJ. 2013 Nov 14;347:f6698. doi: 10.1136/bmj.f6698.
2. MacMahon B, Pugh TF. Epidemiologic Methods (Little, Brown; 1960); reissued as Epidemiology: Principles and Methods (Little, Brown; 1970) (ISBN 0316542598)
3. Taubes, Gary; Mann, Charles C. Epidemiology faces its limits. Science; Jul 14, 1995;269, 5221. Pg. 164-169
4. Willett WC, Stampfer MJ. Current evidence on Healthy Eating. Annu. Rev. Public Health 2013, 34:77-95.
5. Altman DG. Why we need confidence intervals. World J Surg. 2005;29(5):554-6.
6. Willett WC. Dietary fats and coronary heart disease. J Intern Med. 2012 Jul;272(1):13-24. doi: 10.1111/j.1365-2796.2012.02553.x.
7. Ioannidis JP. 2005. Why most published research findings are false. PLoS Med 2:e123.
8. Goodman Steven, Greenland Sander. 2007. Assessing the unreliability of the medical literature: A response to “why most published research findings are false” (Feb 2007). Johns Hopkins University, Dept of biostatistics working papers. Working paper 125. http://biostats.bepress.com/jhubiostat/paper135
9. Goodman S, Greenland S. (2007) Why most published research findings are false: Problems in the analysis. PLoS Med 4(4):e168.doi:10.1371/journal.pmed/0040168
10. Wren JD. Truth, probability, and frameworks. PLoS Med. 2005 Nov;2(11):e361.
11. PLoS Medicine Editors (2005) Minimizing mistakes and embracing uncertainty. PLoS Med 2: e272. doi: 10.1371/journal.pmed.0020272.
12. Shrier I (2005) Power, reliability, and heterogeneous results. PLoS Med 2(11): e386.
13. Wren J (2005) Truth, probability, and frameworks. PLoS Med 2(11): e361.
14. Willett WC. The WHI joins MRFIT: a revealing look beneath the covers. Am J Clin Nutr. 2010;91(4):829-30.
15. Rose G, Hamilton PJ. A randomised controlled trial of the effect on middle-aged men of advice to stop smoking. J Epidemiol Community Health. 1978 Dec;32(4):275-81.
16. Lumley J, Chamberlain C, Dowswell T, Oliver S, Oakley L, Watson L. Interventions for promoting smoking cessation during pregnancy. Cochrane Database Syst Rev. 2009 Jul 8;(3):CD001055. doi: 10.1002/14651858.CD001055.pub3. Review.Update in: Cochrane Database Syst Rev. 2013;10:CD001055.
17. Howard BV, Van Horn L, Hsia J, Manson JE, Stefanick ML, Wassertheil-Smoller S et al. Low-fat dietary pattern and risk of cardiovascular disease: the Women's Health Initiative Randomized Controlled Dietary Modification Trial. JAMA. 2006 Feb 8;295(6):655-66.
18. Multiple Risk Factor Intervention Trial Research Group. Multiple Risk Factor Intervention Trial: risk factor changes and mortality results. JAMA1982;248:1465–77.
19. Martin LJ, Li Q, Melnichouk O, Greenberg C, Minkin S, Hislop G et al. A randomized trial of dietary intervention for breast cancer prevention. Cancer Res. 2011 Jan 1;71(1):123-33. doi: 10.1158/0008-5472.CAN-10-1436.
20. Prentice RL, Caan B, Chlebowski RT, Patterson R, Kuller LH, Ockene JK et al. Low-fat dietary pattern and risk of invasive breast cancer: the Women's Health Initiative Randomized Controlled Dietary Modification Trial. JAMA. 2006 Feb 8;295(6):629-42.
21. Byrne C, Rockett H, Holmes MD. Dietary fat, fat subtypes, and breast cancer risk: lack of an association among postmenopausal women with no history of benign breast disease. Cancer Epidemiol Biomarkers Prev. 2002 Mar;11(3):261-5.
22. Smith-Warner SA, Spiegelman D, Adami HO, Beeson WL, van den Brandt PA, Folsom AR et al.Types of dietary fat and breast cancer: a pooled analysis of cohort studies. Int J Cancer. 2001 Jun 1;92(5):767-74.
23. Sacks FM, Katan M. Randomized clinical trials on the effects of dietary fat and carbohydrate on plasma lipoproteins and cardiovascular disease. Am J Med.2002 Dec 30;113 Suppl 9B:13S-24S.
24. Mozaffarian D, Micha R, Wallace S. Effects on coronary heart disease of increasing polyunsaturated fat in place of saturated fat: a systematic review and meta-analysis of randomized controlled trials. PLoS Med. 2010;7(3):e1000252.
25. Jakobsen MU, O'Reilly EJ, Heitmann BL, Pereira MA, Bälter K, Fraser GE et al. Major types of dietary fat and risk of coronary heart disease: a pooled analysis of 11 cohort studies. Am J Clin Nutr. 2009 May;89(5):1425-32. doi: 10.3945/ajcn.2008.27124.
26. Estruch R, Ros E, Salas-Salvadó J, Covas MI, Corella D, Arós F et al; PREDIMED Study Investigators. Primary prevention of cardiovascular disease with a Mediterranean diet. N Engl J Med. 2013 Apr 4;368(14):1279-90. doi: 10.1056/NEJMoa1200303.
27. Sofi F, Abbate R, Gensini GF, Casini A. Accruing evidence on benefits of adherence to the Mediterranean diet on health: an updated systematic review and meta-analysis. Am J Clin Nutr. 2010 Nov;92(5):1189-96. doi: 10.3945/ajcn.2010.29673.
28. Shai I, Schwarzfuchs D, Henkin Y, Shahar DR, Witkow S, Greenberg I et al. Dietary Intervention Randomized Controlled Trial (DIRECT) Group. Weight loss with a low-carbohydrate, Mediterranean, or low-fat diet. N Engl J Med. 2008 Jul 17;359(3):229-41. doi: 10.1056/NEJMoa0708681.Erratum in: N Engl J Med. 2009 Dec 31;361(27):2681.
29. Esposito K, Kastorini CM, Panagiotakos DB, Giugliano D. Mediterranean diet and weight loss: meta-analysis of randomized controlled trials. Metab Syndr Relat Disord. 2011;9(1):1-12.
30. Martínez-González MA, García-Arellano A, Toledo E, Salas-Salvadó J, Buil-Cosiales P, Corella D et al; PREDIMED Study Investigators. A 14-item Mediterranean diet assessment tool and obesity indexes among high-risk subjects: the PREDIMED trial. PLoS One. 2012;7(8):e43134.
31. Malik VS, Pan A, Willett WC, Hu FB. Sugar-sweetened beverages and weight gain in children and adults: a systematic review and meta-analysis. Am J Clin Nutr.2013;98(4):1084-102.
32. Malik VS, Popkin BM, Bray GA, Després JP, Willett WC, Hu FB. Sugar-sweetened beverages and risk of metabolic syndrome and type 2 diabetes: a meta-analysis.Diabetes Care. 2010;33(11):2477-83.
33. Perez-Pozo SE, Schold J, Nakagawa T, Sánchez-Lozada LG, Johnson RJ, Lillo JL. Excessive fructose intake induces the features of metabolic syndrome in healthy adult men: role of uric acid in the hypertensive response. Int J Obes (Lond).2010;34(3):454-61.
34. Livesey G, Taylor R, Livesey H, Liu S. Is there a dose-response relation of dietary glycemic load to risk of type 2 diabetes? Meta-analysis of prospective cohort studies. Am J Clin Nutr. 2013;97(3):584-96.
35. Chiasson JL, Josse RG, Gomis R, Hanefeld M, Karasik A, Laakso M; STOP-NIDDM Trail Research Group. Acarbose for prevention of type 2 diabetes mellitus: the STOP-NIDDM randomised trial. Lancet. 2002 Jun 15;359(9323):2072-7.
36. Kelly S, Frost G, Whittaker V, Summerbell C. Low glycaemic index diets for coronary heart disease. Cochrane Database Syst Rev. 2004;(4):CD004467.
37. Mirrahimi A, de Souza RJ, Chiavaroli L, Sievenpiper JL, Beyene J, Hanley AJ et al. Associations of glycemic index and load with coronary heart disease events: a systematic review and meta-analysis of prospective cohorts. J Am Heart Assoc. 2012;1(5):e000752.doi:10.1161/JAHA.112.000752.
38. Gu D, Zhao Q, Chen J, Chen JC, Huang J, Bazzano LA et al. Reproducibility of blood pressure responses to dietary sodium and potassium interventions: the GenSalt study.Hypertension. 2013;62(3):499-505.
39. Sacks FM, Willett WC, Smith A, Brown LE, Rosner B, Moore TJ. Effect on blood pressure of potassium, calcium, and magnesium in women with low habitual intake. Hypertension. 1998 Jan;31(1):131-8.
40. Ascherio A, Hennekens C, Willett WC, Sacks F, Rosner B, Manson J et al. Prospective study of nutritional factors, blood pressure, and hypertension among US women. Hypertension. 1996 May;27(5):1065-72.
41. Aburto NJ, Hanson S, Gutierrez H, Hooper L, Elliott P, Cappuccio FP. Effect of increased potassium intake on cardiovascular risk factors and disease: systematic review and meta-analyses. BMJ. 2013;346:f1378. doi: 10.1136/bmj.f1378.
42. Giovannucci E, Stampfer MJ, Colditz GA, Hunter DJ, Fuchs C, Rosner BA et al. Multivitamin use, folate, and colon cancer in women in the Nurses' Health Study. Ann Intern Med. 1998;129(7):517-24.
43. Gaziano JM, Sesso HD, Christen WG, Bubes V, Smith JP, MacFadyen J et al. Multivitamins in the prevention of cancer in men:the Physicians' Health Study II randomized controlled trial. JAMA. 2012;308(18):1871-80.
44. Vartiainen E, Jousilahti P, Alfthan G, Sundvall J, Pietinen P, Puska P. Cardiovascular risk factor changes in Finland, 1972-1997. Int J Epidemiol. 2000;29(1):49-56.
45. Keys AC, Aravanis H, Blackburn R et al. Seven countries. A multivariate analysis of death and coronary heart disease. 1980. Cambridge: Harvard University Press.
46. Dawber TR, Meadors GF, Moore FE, Jr.: Epidemiological approaches to heart disease: the Framingham Study. Am J Public Health 1951; 41(3):279-286.
47. Luepker RV, Murray DM, Jacobs DR Jr, Mittelmark MB, Bracht N, Carlaw R et al. Community education for cardiovascular disease prevention: risk factor changes in the Minnesota Heart Health Program. Am J Public Health. 1994;84(9):1383-93.
48. Mozaffarian D, Katan MB, Ascherio A, Stampfer MJ, Willett WC (2006). "Trans Fatty Acids and Cardiovascular Disease". New England Journal of Medicine 354 (15): 1601–1613.
49. Mozaffarian D, Aro A, Willett WC. Health effects of trans-fatty acids:experimental and observational evidence. Eur J Clin Nutr. 2009 May;63 Suppl2:S5-21. doi: 10.1038/sj.ejcn.1602973.
Competing interests:
No competing interests
16 May 2014
Shanshan Li
Postdoctoral Research Fellow
Alan Flint, Jennifer Pai, John P. Forman, Frank B. Hu, Walter C. Willett, Kathryn M. Rexrode, Kenneth J. Mukamal, Eric B. Rimm
Rapid Response:
Re: Implausible results in human nutrition research
We read with great interest Dr. Ioannidis’s paper on “Implausible results in human nutrition research: Definitive solutions won’t come from another million observational papers or small randomized trials” (1). While we can appreciate his editorial on the subject, this general discussion on the strengths and limitations of observational and experimental studies is not unique to nutrition and is commonplace in textbooks on epidemiological methods dating back to MacMahon and Pugh’s first text on the subject in 1970 (2). Strong commentary on the limitations of epidemiology in the study of nutrition can be traced back to Taubes’ article in Science in 1995 (3). A thorough rehashing of his arguments goes beyond the scope of this response, but in all areas of epidemiology (and other areas of scientific study), false positive and false negative results inevitably occur, and many studies lack replication. We discuss some of the main points below.
Dr. Ioannidis’s comment that “Many findings are entirely implausible” is not helpful as implausible finding occur by chance or other reasons in almost all areas of science, and conclusions should not be based on a single finding but rather the plausibility given all available evidence and on replication (1). In nutritional research, we usually evaluate the evidence from animal/mechanistic experiments, biological/metabolic findings, and epidemiological/intervention studies together to reach conclusions (4). No single study should stand on its own, especially now that decades of nutritional research are available. Similarly, no single editorial should completely dismiss the great value the last 50 years of research has provided. Dr. Ioannidis selectively picked a few estimates from the vast amount of nutrition literature without any context. More importantly, he did not include the 95% confidence intervals surrounding those estimates. The 95% CIs can provide important information on both certainty and uncertainty of the point estimates (5). In evidence-based nutrition, meta-analyses and systematic reviews instead of findings from a single study are used to develop recommendations or guidelines. Therefore, consistency and replications of the findings across different populations are extremely important.
If we use dietary fat and heart disease as a first example, the weak and inconsistent results mainly derive from early studies, which were not designed to investigate the fat-CHD association. However, they should not be interpreted as providing strong negative evidence (6). The limitations in early studies include small sample size; use of a single 24-hour recall for dietary assessment; lack of updated dietary measurement during follow-up; and no adjustment for total energy intake or other dietary factors. More recent large prospective cohort studies have addressed these limitations. Results from high quality observational studies correspond well with randomized controlled trials (Table 1). Interestingly, in a publication from 2005, Dr. Ioannidis made the similarly dramatic claim that “Most biomedical research findings are false for most research designs and for most fields” (7). Goodman and Greenland (and others) have provided detailed responses to this claim and identified the logical flaws of Dr. Ioannidis’ assertion (8-13).
Dr. Ioannidis concluded that in future we would need randomized controlled trials (RCTs) 10 times the sample size of the Prevención con Dieta Mediterránea (PREDIMED) study (1). Interestingly, the majority of nutrition trials, even the size of PREDIMED, would not have been proposed or conducted had there not been very compelling evidence of the benefits of the Mediterranean diet, olive oil, and nuts from short term trials with intermediate endpoint and observational studies with coronary heart disease - the exact studies Dr. Ioannidis argues against performing. Does Dr. Ioannidis suggest that we conduct randomized trials 10 times the size of PREDIMED based on no more than simple conjuring of hypothetical biological pathways connecting nutrition with long term health?
Contrary to common beliefs, RCTs are not immune to confounding and serious bias even if they are large, and they can provide seriously misleading answers (14). For example, RCT's of smoking cessation showed no benefit on mortality (15), very low birth weight, neonatal death or perinatal mortality (16). Also, studies such as the Women’s Health Initiative, with a $400 million arm to test the benefits of a very low fat diet, failed to test the fat hypothesis due to low compliance with the dietary intervention (17). The earlier Multiple Risk Factor Intervention Trial (MRFIT) also failed to test its original hypothesis due to poor adherence and found no significant effect of an intervention combining diet, smoking cessation and hypertension treatment on coronary disease (18). These issues will not simply disappear by increasing sample size and they will worsen with longer follow-up(14). Randomized trials are randomized and free of confounding only at baseline, and their interpretation is complicated by attrition and non-compliance that is subject to confounding and selection bias - the same issues we are concerned about in observational studies.
Finally, Dr. Ioannidis comment that “Definitive solutions won’t come from another million observational papers or small randomized trials” (1) over simplifies the conduct of nutrition research and shows a deeper misunderstanding of the field. Because of the complex nature of our field, conclusions need to be based on the broader totality of evidence from human observational and clinical studies. In the past decades, cardiovascular mortality has decreased dramatically in Finland, US, and other developed countries, and more than half of the decline is attributable to improvement in diet and lifestyle factors. The landmark North Karelia study (44), the Seven Countries Study (45), the Framingham Heart study (46), the Minnesota Heart Health Program (47), and many other studies have shown that his claim of implausible nutrition finding does not hold water. A recent example would be trans fat. Well conducted long term observational studies and small randomized trials provided consistent and convincing evidence of the adverse effects of trans fat on lipid levels, inflammation, endothelial dysfunction, and significantly increased risk of coronary heart disease (48, 49). Despite the lack of large, long-term trials (48, 49) important changes were made to nutritional labels and policies across the globe, and food companies have removed up to 80% of trans fat in foods in the US. This clear public health advance was made with just the evidence that Dr. Ioannidis scorned; millions of premature deaths will be prevented that would not have been had we waited to conduct a mega-trial of trans fat to prove harm, and which could easily provide misleading results if it had the same fate as the WHI or MRFIT trials.
Reference:
1. Ioannidis JP. Implausible results in human nutrition research. BMJ. 2013 Nov 14;347:f6698. doi: 10.1136/bmj.f6698.
2. MacMahon B, Pugh TF. Epidemiologic Methods (Little, Brown; 1960); reissued as Epidemiology: Principles and Methods (Little, Brown; 1970) (ISBN 0316542598)
3. Taubes, Gary; Mann, Charles C. Epidemiology faces its limits. Science; Jul 14, 1995;269, 5221. Pg. 164-169
4. Willett WC, Stampfer MJ. Current evidence on Healthy Eating. Annu. Rev. Public Health 2013, 34:77-95.
5. Altman DG. Why we need confidence intervals. World J Surg. 2005;29(5):554-6.
6. Willett WC. Dietary fats and coronary heart disease. J Intern Med. 2012 Jul;272(1):13-24. doi: 10.1111/j.1365-2796.2012.02553.x.
7. Ioannidis JP. 2005. Why most published research findings are false. PLoS Med 2:e123.
8. Goodman Steven, Greenland Sander. 2007. Assessing the unreliability of the medical literature: A response to “why most published research findings are false” (Feb 2007). Johns Hopkins University, Dept of biostatistics working papers. Working paper 125. http://biostats.bepress.com/jhubiostat/paper135
9. Goodman S, Greenland S. (2007) Why most published research findings are false: Problems in the analysis. PLoS Med 4(4):e168.doi:10.1371/journal.pmed/0040168
10. Wren JD. Truth, probability, and frameworks. PLoS Med. 2005 Nov;2(11):e361.
11. PLoS Medicine Editors (2005) Minimizing mistakes and embracing uncertainty. PLoS Med 2: e272. doi: 10.1371/journal.pmed.0020272.
12. Shrier I (2005) Power, reliability, and heterogeneous results. PLoS Med 2(11): e386.
13. Wren J (2005) Truth, probability, and frameworks. PLoS Med 2(11): e361.
14. Willett WC. The WHI joins MRFIT: a revealing look beneath the covers. Am J Clin Nutr. 2010;91(4):829-30.
15. Rose G, Hamilton PJ. A randomised controlled trial of the effect on middle-aged men of advice to stop smoking. J Epidemiol Community Health. 1978 Dec;32(4):275-81.
16. Lumley J, Chamberlain C, Dowswell T, Oliver S, Oakley L, Watson L. Interventions for promoting smoking cessation during pregnancy. Cochrane Database Syst Rev. 2009 Jul 8;(3):CD001055. doi: 10.1002/14651858.CD001055.pub3. Review.Update in: Cochrane Database Syst Rev. 2013;10:CD001055.
17. Howard BV, Van Horn L, Hsia J, Manson JE, Stefanick ML, Wassertheil-Smoller S et al. Low-fat dietary pattern and risk of cardiovascular disease: the Women's Health Initiative Randomized Controlled Dietary Modification Trial. JAMA. 2006 Feb 8;295(6):655-66.
18. Multiple Risk Factor Intervention Trial Research Group. Multiple Risk Factor Intervention Trial: risk factor changes and mortality results. JAMA1982;248:1465–77.
19. Martin LJ, Li Q, Melnichouk O, Greenberg C, Minkin S, Hislop G et al. A randomized trial of dietary intervention for breast cancer prevention. Cancer Res. 2011 Jan 1;71(1):123-33. doi: 10.1158/0008-5472.CAN-10-1436.
20. Prentice RL, Caan B, Chlebowski RT, Patterson R, Kuller LH, Ockene JK et al. Low-fat dietary pattern and risk of invasive breast cancer: the Women's Health Initiative Randomized Controlled Dietary Modification Trial. JAMA. 2006 Feb 8;295(6):629-42.
21. Byrne C, Rockett H, Holmes MD. Dietary fat, fat subtypes, and breast cancer risk: lack of an association among postmenopausal women with no history of benign breast disease. Cancer Epidemiol Biomarkers Prev. 2002 Mar;11(3):261-5.
22. Smith-Warner SA, Spiegelman D, Adami HO, Beeson WL, van den Brandt PA, Folsom AR et al.Types of dietary fat and breast cancer: a pooled analysis of cohort studies. Int J Cancer. 2001 Jun 1;92(5):767-74.
23. Sacks FM, Katan M. Randomized clinical trials on the effects of dietary fat and carbohydrate on plasma lipoproteins and cardiovascular disease. Am J Med.2002 Dec 30;113 Suppl 9B:13S-24S.
24. Mozaffarian D, Micha R, Wallace S. Effects on coronary heart disease of increasing polyunsaturated fat in place of saturated fat: a systematic review and meta-analysis of randomized controlled trials. PLoS Med. 2010;7(3):e1000252.
25. Jakobsen MU, O'Reilly EJ, Heitmann BL, Pereira MA, Bälter K, Fraser GE et al. Major types of dietary fat and risk of coronary heart disease: a pooled analysis of 11 cohort studies. Am J Clin Nutr. 2009 May;89(5):1425-32. doi: 10.3945/ajcn.2008.27124.
26. Estruch R, Ros E, Salas-Salvadó J, Covas MI, Corella D, Arós F et al; PREDIMED Study Investigators. Primary prevention of cardiovascular disease with a Mediterranean diet. N Engl J Med. 2013 Apr 4;368(14):1279-90. doi: 10.1056/NEJMoa1200303.
27. Sofi F, Abbate R, Gensini GF, Casini A. Accruing evidence on benefits of adherence to the Mediterranean diet on health: an updated systematic review and meta-analysis. Am J Clin Nutr. 2010 Nov;92(5):1189-96. doi: 10.3945/ajcn.2010.29673.
28. Shai I, Schwarzfuchs D, Henkin Y, Shahar DR, Witkow S, Greenberg I et al. Dietary Intervention Randomized Controlled Trial (DIRECT) Group. Weight loss with a low-carbohydrate, Mediterranean, or low-fat diet. N Engl J Med. 2008 Jul 17;359(3):229-41. doi: 10.1056/NEJMoa0708681.Erratum in: N Engl J Med. 2009 Dec 31;361(27):2681.
29. Esposito K, Kastorini CM, Panagiotakos DB, Giugliano D. Mediterranean diet and weight loss: meta-analysis of randomized controlled trials. Metab Syndr Relat Disord. 2011;9(1):1-12.
30. Martínez-González MA, García-Arellano A, Toledo E, Salas-Salvadó J, Buil-Cosiales P, Corella D et al; PREDIMED Study Investigators. A 14-item Mediterranean diet assessment tool and obesity indexes among high-risk subjects: the PREDIMED trial. PLoS One. 2012;7(8):e43134.
31. Malik VS, Pan A, Willett WC, Hu FB. Sugar-sweetened beverages and weight gain in children and adults: a systematic review and meta-analysis. Am J Clin Nutr.2013;98(4):1084-102.
32. Malik VS, Popkin BM, Bray GA, Després JP, Willett WC, Hu FB. Sugar-sweetened beverages and risk of metabolic syndrome and type 2 diabetes: a meta-analysis.Diabetes Care. 2010;33(11):2477-83.
33. Perez-Pozo SE, Schold J, Nakagawa T, Sánchez-Lozada LG, Johnson RJ, Lillo JL. Excessive fructose intake induces the features of metabolic syndrome in healthy adult men: role of uric acid in the hypertensive response. Int J Obes (Lond).2010;34(3):454-61.
34. Livesey G, Taylor R, Livesey H, Liu S. Is there a dose-response relation of dietary glycemic load to risk of type 2 diabetes? Meta-analysis of prospective cohort studies. Am J Clin Nutr. 2013;97(3):584-96.
35. Chiasson JL, Josse RG, Gomis R, Hanefeld M, Karasik A, Laakso M; STOP-NIDDM Trail Research Group. Acarbose for prevention of type 2 diabetes mellitus: the STOP-NIDDM randomised trial. Lancet. 2002 Jun 15;359(9323):2072-7.
36. Kelly S, Frost G, Whittaker V, Summerbell C. Low glycaemic index diets for coronary heart disease. Cochrane Database Syst Rev. 2004;(4):CD004467.
37. Mirrahimi A, de Souza RJ, Chiavaroli L, Sievenpiper JL, Beyene J, Hanley AJ et al. Associations of glycemic index and load with coronary heart disease events: a systematic review and meta-analysis of prospective cohorts. J Am Heart Assoc. 2012;1(5):e000752.doi:10.1161/JAHA.112.000752.
38. Gu D, Zhao Q, Chen J, Chen JC, Huang J, Bazzano LA et al. Reproducibility of blood pressure responses to dietary sodium and potassium interventions: the GenSalt study.Hypertension. 2013;62(3):499-505.
39. Sacks FM, Willett WC, Smith A, Brown LE, Rosner B, Moore TJ. Effect on blood pressure of potassium, calcium, and magnesium in women with low habitual intake. Hypertension. 1998 Jan;31(1):131-8.
40. Ascherio A, Hennekens C, Willett WC, Sacks F, Rosner B, Manson J et al. Prospective study of nutritional factors, blood pressure, and hypertension among US women. Hypertension. 1996 May;27(5):1065-72.
41. Aburto NJ, Hanson S, Gutierrez H, Hooper L, Elliott P, Cappuccio FP. Effect of increased potassium intake on cardiovascular risk factors and disease: systematic review and meta-analyses. BMJ. 2013;346:f1378. doi: 10.1136/bmj.f1378.
42. Giovannucci E, Stampfer MJ, Colditz GA, Hunter DJ, Fuchs C, Rosner BA et al. Multivitamin use, folate, and colon cancer in women in the Nurses' Health Study. Ann Intern Med. 1998;129(7):517-24.
43. Gaziano JM, Sesso HD, Christen WG, Bubes V, Smith JP, MacFadyen J et al. Multivitamins in the prevention of cancer in men:the Physicians' Health Study II randomized controlled trial. JAMA. 2012;308(18):1871-80.
44. Vartiainen E, Jousilahti P, Alfthan G, Sundvall J, Pietinen P, Puska P. Cardiovascular risk factor changes in Finland, 1972-1997. Int J Epidemiol. 2000;29(1):49-56.
45. Keys AC, Aravanis H, Blackburn R et al. Seven countries. A multivariate analysis of death and coronary heart disease. 1980. Cambridge: Harvard University Press.
46. Dawber TR, Meadors GF, Moore FE, Jr.: Epidemiological approaches to heart disease: the Framingham Study. Am J Public Health 1951; 41(3):279-286.
47. Luepker RV, Murray DM, Jacobs DR Jr, Mittelmark MB, Bracht N, Carlaw R et al. Community education for cardiovascular disease prevention: risk factor changes in the Minnesota Heart Health Program. Am J Public Health. 1994;84(9):1383-93.
48. Mozaffarian D, Katan MB, Ascherio A, Stampfer MJ, Willett WC (2006). "Trans Fatty Acids and Cardiovascular Disease". New England Journal of Medicine 354 (15): 1601–1613.
49. Mozaffarian D, Aro A, Willett WC. Health effects of trans-fatty acids:experimental and observational evidence. Eur J Clin Nutr. 2009 May;63 Suppl2:S5-21. doi: 10.1038/sj.ejcn.1602973.
Competing interests: No competing interests