In January, U.S. officials released a new set of Dietary Guidelines—broad advice on how the nation should eat. The new guidelines included some significant changes from previous versions, including the recommendation that no more than 10% of a person’s daily calories come from added sugars. But there were also some omissions, which have drawn criticism from nutrition scientists at Harvard T.H. Chan School of Public Health. On Thursday, March 24, Vasanti Malik, a research scientist in the Department of Nutrition, answered questions about the new guidelines during a reddit AMA (Ask Me Anything).
Here some highlights from that AMA:
What do you think is the greatest contributing factor to the rampant obesity rate in the U.S.?
The increase in calories over time from increasing portion sizes, but also the increase in intake of refined carbohydrates and added sugar. In the late 1970’s the dietary guidelines recommended to decrease intake of fat for health, but a consequence of this was that people increased intake of refined carbohydrates and added sugar. Both of these factors have been associated with weight gain and risk of related chronic diseases.
Is it true that the U.S. Dietary Guidelines are heavily influenced by lobbyists?
This is an important question. To answer this question, I think it’s important to briefly explain how the Dietary Guidelines are created. First, an advisory committee (appointed by the U.S. Department of Agriculture (USDA) and Department of Health and Human Services (HHS)) comprised of scientists and experts in the field review the evidence base to establish recommendations that are then given to the USDA and HHS for them to base the actual recommendations on (you can read the full report here). Because the advisory committee’s recommendations and the actual Guidelines differ to some degree it appears that there are various forces including lobbyists involved in determining the recommendations. We have discussed this in more detail on our website, specifically recommendations regarding red meat and sugar-sweetened beverages, which were omitted from the final Guidelines. The advisory report raised the issue of environmental sustainability in our diet, such as [reducing red meat consumption] and eating a more plant-based diet, but that specific recommendation is not included in the final Guidelines.
How would one from a low socioeconomic background participate in good nutritional health? Is calorie intake more important than the nutritional value of the calorie source in some cases?
This tends to be true in some settings such as in low- and middle-income countries, but tends to be less true in the U.S. and other high-income countries. In contrast, what we tend to see is overconsumption of cheap, processed, or fast foods that are high in energy but low in nutritional value—leading to obesity. People aren’t necessarily starving for calories, but rather for healthful foods and nutrients. Population strategies to help this issue include the use of Supplemental Nutrition Assistance Program (SNAP) benefits at farmer’s markets, reducing the cost of fruit and vegetables through subsidies, and elimination of [areas with limited access to full-service grocery stores or supermarkets]. Education in low-income neighborhoods is also key here. One study found that consuming a healthy diet can be cheaper than an unhealthy diet.
Why do keto- and paleo-style diets (high fat, low carb) get such a bad reputation when there is so much anecdotal evidence that they improve health? The main criticisms seem to revolve around the inability of some people being able to stick to them.
There seem to be a number of questions about paleo and other popular diets. The issue here is exactly what you mention, there may be anecdotal evidence but there is very limited scientific evidence to support these types of diets. One issue is, of course, adherence as you mention. If people are not able to adhere to a given diet then its effectiveness is questionable. Aside from effectiveness of the diet for weight management there are other concerns with the paleo diet, such as adverse health effects from restricting carbohydrates including whole grains, some fruits, and dairy. High protein diets in general can also be adverse for kidney function in the long term. When it comes to dietary patterns for weight and also overall health, evidence points to consuming a Mediterranean–style diet, which also tends to more palatable than other diets.
Since a number of questions have appeared regarding diets in general, I thought I would add that there is very limited evidence to support a low-fat diet which has been the mantra for many years and that the evidence is influenced by many factors including the intensity of the intervention group relative to the control group. Please take a look at our recent meta-analysis and systematic review on this topic and here’s a link to an article on this study.