Posts Tagged ‘New York Times’

Why It Is So Hard to Figure Out What to Eat

Most diet trials in the best journals fail even the most basic of quality control measures.

By David S. Ludwig and

Drs. Ludwig and Heymsfield are physicians and health scholars.

Credit…Benoit Tardif

Most diet trials in the best journals fail even the most basic of quality control measures. That’s the finding of a study by us published today on JAMA Network Open.

Investigators receiving funding for any clinical trial from the National Institutes of Health must register in advance what they plan to test, among other design features, to ensure that the data are fairly analyzed. Comparing the original registries with the final published studies, we found that diet trials in the past decade were about four times as likely as drug trials to have a discrepancy in the main outcome or measurement — raising concern for bias.

This quality-control problem of diet trials in comparison to ones on pharmaceuticals leads to a bigger issue: underinvestment in nutrition research and in how we tackle the mysteries of a healthy diet.

Although the problems with observational studies have received much attention (“Association doesn’t prove causation,” as scientists say), clinical trials can suffer from equally important limitations. In a clinical trial, investigators assign volunteers to receive different treatments — such as a low-carbohydrate versus low-fat diet — ideally in random order. Beyond registry issues, trials may provide misleading results for many reasons, including small size, short duration and weak interventions (they lack power to actually make the intended change in behavior).

These failures are disturbing because epidemics of diet-related disease will shorten life expectancy and impose huge economic costs on the United States in coming years. We continue to lack effective dietary prevention, in part because clinical trials have been too poorly designed and conducted to reach definitive conclusions. We’re still debating questions that have raged for decades: Should we focus on reducing carbs or fat? Is red meat harmful? Is sugar toxic? What about artificially sweetened beverages or moderate amounts of alcohol?

High-quality trials are hard to do because diets, and the behavior of humans who consume them, are so complicated. A single meal might have dozens of nutrients and hundreds of other bioactive substances that interact in unknown ways. Furthermore, if the diet being studied increases intake from one food category, people may eat less from other food categories, making it difficult to attribute results to any specific dietary component.

Diet trials also require subjects to change their eating habits, a far greater challenge than taking a pill.

Consider a trial for a promising cancer treatment in which participants assigned to receive the drug didn’t take it as intended. If the drug group showed no benefit over the placebo group, we wouldn’t automatically assume the drug lacked promise. We would conclude that the study failed and that stronger methods (medication organizer trays and daily text message reminders, say) are needed to make sure the drug is properly used so that we can see if it works. Yet the illogical assumption that a diet didn’t work is commonly made when volunteers in weak trials do not follow the assigned diets.

Short diet trials, the great majority of those done, raise special concerns. Many people can lose weight by restricting calories at first, but few can maintain substantial weight loss that way. After a few days or weeks, the body begins to resist calorie deprivation, with rising hunger and slowing metabolism. Making matters more complicated, it takes several weeks to adapt to major changes in nutrients. For these reasons, short-term trials may have little relevance to understanding how diet affects health over the long term.

It would be like studying an intensive exercise program — including long runs, calisthenics and strenuous sports — among sedentary volunteers for just six days. The investigators might find that the program made the volunteers sore, tired and weak. However, a six-month trial, allowing adequate time to adapt to the new regimen, would reach the opposite conclusion, revealing the real benefits of physical activity.

Despite their greater difficulties, diet trials receive far less funding than drug trials, especially considering that poor diet is the leading risk factor for premature death. Few big companies stand to profit directly from dietary treatments for chronic diseases. Consequently, typical diet trials must get by on shoestring budgets, rarely exceeding a few hundred thousand dollars, compared with drug trials that may cost several hundred million dollars. Without adequate support, quality inevitably suffers. Diet trials of adequate size, duration and intervention strength rarely get done.

This problem has special relevance now, as the Dietary Guidelines Advisory Committee reviews the science in preparation for new Department of Agriculture recommendations to the public in 2020. Among thousands of scientific articles initially screened, only a small proportion so far have passed strict quality criteria for inclusion in committee deliberations. And ultimately, recommendations to the public can be no stronger than the science on which they rely.

Which doesn’t mean that all nutrition research is unreliable. High-quality observational studies and clinical trials provide strong evidence for the benefits of whole carbohydrates (nonstarchy vegetables, fruits, legumes, minimally processed intact grains) over highly processed, fast-digesting carbohydrates (refined grains, potato products and added sugar). We also know that nuts, olive oil and avocado protect against chronic disease, contrary to dietary recommendations during the low-fat diet era, as embodied by the 1992 Food Guide Pyramid.

We need a sort of Manhattan Project to find definitive answers to the epidemics of diet-related disease. Nutrition research to prevent disease must have the same quality and rigor as pharmaceutical research to treat disease. Building the necessary scientific infrastructure will require sustained investment by government and philanthropic organizations, but the amounts involved would total a fraction of a cent for every dollar spent treating diet-related conditions like obesity, Type 2 diabetes and cardiovascular disease.

Study authors and the media can help by avoiding the tendency to overstate the results of weak research, contributing to public confusion. And the public has a critical role to play, not only demanding government action but also volunteering for diet studies.

No other factor approaches the importance of diet for public health. To reduce the human toll of chronic disease, we must upgrade the quality of nutrition research. The financial investment required will yield huge returns in medical cost savings.

Read Full Post »

Venture capital investment was down slightly in the third quarter, according to the MoneyTree Report released Saturday from PricewaterhouseCoopers and the National Venture Capital Association. Venture capitalists put $7.7 billion into 1,033 deals, a decrease of 7 percent from the second quarter.

The third quarter of the year is generally slower for venture investing, and the analysts who produced the report said that the economic crisis is not yet affecting venture numbers. In future quarters, though, the industry will probably see a dip in investing, said Tracy T. Lefteroff, global managing partner of the venture capital practice at PricewaterhouseCoopers.

For now, “the venture industry is very much open for business,” said John S. Taylor, vice president of research at the National Venture Capital Association.

Click here for the full article

Read Full Post »