Most people believe that a good diet is a cornerstone of vibrant health. Many also take supplements as dietary insurance to make sure that they get the nutrients they need. A massive new review of 277 clinical trials including close to a million participants has concluded that most diets and supplements are useless (Annals of Internal Medicine, July 9, 2019). Even those promoted to improve heart health do nothing to improve longevity or reduce complications.
What’s Wrong with Diets and Supplements?
The investigators examined the recommendations put forward in the US dietary guidelines. To find out how well the evidence supports these ideas, they looked for randomized controlled trials and meta-analyses of diets and supplements. They certainly found a great deal of data, but not all the studies were of the same quality. Most of the studies did not find that the intervention studied resulted in better survival or fewer heart attacks.
The investigators analyzed results for 16 different types of supplements and eight kinds of dietary interventions. These included approaches such as reducing saturated fat or increasing omega-3 alpha linolenic acid intake. In addition, they reviewed data on the Mediterranean diet.
They concluded that there is reasonable evidence that reducing salt intake lowers the likelihood of premature death. It appears to protect people with high blood pressure from heart problems. In addition, folic acid might reduce the risk of stroke according to these data. However, a large study in China had an outsize effect on this analysis. When it comes to stroke, they found a greater risk among people taking a combination of calcium and vitamin D. None of the other diets and supplements offered significant advantages or risks.
What About the Mediterranean Diet?
This conclusion is especially surprising with regard to the Mediterranean diet. PubMed has more than 6,000 entries on this high-vegetable, high-olive oil, low-processed food approach to eating. Most of the published studies show benefits such as reducing the risk of diabetes (Endocrine, April 2017). Other studies suggest that a Mediterranean diet benefits brain health (Ageing Research Reviews, March 2015). Moreover, analyses indicate that people eating the Mediterranean way are less prone to cancer (Cancer Genomics & Proteomics, Nov-Dec. 2017). Consequently, we are surprised that the Mediterranean diet appeared useless in the current analysis.
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Dispense with Diets and Supplements?
The editors of the Annals of Internal Medicine invited two prominent experts from the Scripps Clinic in La Jolla, CA, to write a commentary on this research. Drs. Amitabh Pandey and Eric Topol were skeptical of the value of supplements, but also of some of the conclusions of the analysis.
Among other objections, they pointed to the problems in the data linking sodium intake and heart problems:
“A longitudinal study of nearly 95 000 people from 18 countries lasting more than 8 years showed an inverse correlation between sodium intake and cardiovascular outcomes…
“With regard to salt intake, Messerli and colleagues have noted that “with an average lifespan of 87.3 years, women in Hong Kong top life expectancy worldwide despite consuming an average of 8-9 g of salt per day.” (10). This exemplifies the problem of amalgamating data from people and cultures with markedly different diet and supplement baselines.”
“Perhaps, however, the biggest difference that needs to be considered in the future is the individual. Only recently with machine learning of large data sets, which include multimodal data on physical activity, sleep, medications, demographic characteristics, intake and timing of all foods and beverages, and gut microbiome constituents, have we begun to learn that the use of any specific diet or supplement is likely to have markedly heterogeneous effects. Testing any diet or supplement in a broad population without acknowledging interindividual variability seems like a recipe for failure, especially because most trials are not randomized, are not of sufficient duration, or do not have enough hard outcome events.
“Unfortunately, the current study leaves us with the same foggy conditions that we started with. Until these conditions clear, it would be reasonable to hold off on any supplement or diet modification in all guidelines and recommendations.”
We agree that abandoning efforts to include more vegetables and fruits in our daily fare seems premature. Giving up on supplements doesn’t make sense for everybody either. You can learn more about the pros and cons of supplements for specific health conditions in Dr. Tieraona Low Dog’s excellent book, Fortify Your Life: Your Guide to Vitamins, Minerals, and More.
Terry Graedon, PhD, is a medical anthropologist and co-host of The People’s Pharmacy radio show, co-author of The People’s Pharmacy syndicated newspaper columns and numerous books, and co-founder of The People’s Pharmacy website. Terry taught in the Duke University School of Nursing and was an adjunct assistant professor in the Department of Anthropology. She is a Fellow of the Society of Applied Anthropology. Terry is one of the country's leading authorities on the science behind folk remedies. Read Terry's Full Bio.
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Khan SU et al, "Effects of nutritional supplements and dietary interventions on cardiovascular outcomes: An umbrella review and evidence map." Annals of Internal Medicine, July 9, 2019. DOI: 10.7326/M19-0341
Pandey AC & Topol EJ, "Dispense with supplements for improving heart outcomes." Annals of Internal Medicine, July 9, 2019. DOI: 10.7326/M19-1498
Esposito K et al, "Mediterranean diet for type 2 diabetes: Cardiometabolic benefits." Endocrine, April 2017. DOI: 10.1007/s12020-016-1018-2
Yannakoulia M et al, "Cognitive health and Mediterranean diet: Just diet or lifestyle pattern?" Ageing Research Reviews, March 2015. DOI: 10.1016/j.arr.2014.10.003
Barak Y & Fridman D, "Impact of Mediterranean diet on cancer: Focused literature review." Cancer Genomics & Proteomics, Nov-Dec. 2017. DOI: 10.21873/cgp.20050
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