Tuesday, February 27, 2018

Short Take: Calories Matter in Weight Loss, Despite Some Recent Headlines

A recently published clinical trial out of Stanford University found that high-quality low-fat and high-quality low-carbohydrate diets could be equally effective for weight loss.

It was a positive finding from a well-designed study.

Many news headlines about the study, however, focused on something else entirely: that calories don't matter for weight loss. Some examples:

The problem is: The study didn't really find that.

In the trial, approximately 600 overweight and obese adults were randomly assigned to one of two diet groups (low-fat or low-carbohydrate) and followed over a 12-month period.  During the study, participants attended regular nutrition classes where emphasis was placed on healthy, high-quality foods – such as whole grains, healthy fats, and minimally processed foods.

Participants were not specifically instructed to lower their calorie intake.

At the end of the study, each group had lost similar amounts of weight. The low-fat group dropped around 12 pounds, and the low-carbohydrate group dropped around 13 pounds. 

So, each group lost weight without being instructed to cut calories:  What's wrong with the "calories don't matter"-themed headlines?

A couple of things.

First, calorie counting was not a subject of study of the trial.   Clinical trials are designed to assess very specific things.  Because calorie counting was not something one group in the study did and another group in the study did not do, no conclusions can be made about its possible impact – or lack of impact –  on weight loss. Any headline implying otherwise is reaching beyond the findings of the current study.  

On top of that, while it’s true that participants were not coached to reduce their calorie intake, that does not mean that they did not eat fewer calories.  In fact, each diet group ate an average of 500 – 600 fewer calories per day during the course of the study than at the start of the study.  That is a large deficit that would lead to weight loss over time. 

For both of these reasons, it's inaccurate to imply that the study found that calories, and counting calories, aren't important for weight loss.

Of course, diet quality is important.  A largely plant-based diet that focuses on fruits, vegetables, whole grains, and healthy fats has long been shown to lower the risk of many diseases and help with weight control.

But diet quantity is key.  To lose weight, we need to take in fewer calories than we expend - whether we count them or not.

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Thursday, February 15, 2018

New Diet Study Finds "Ultra-Processed" Foods May Be Linked to Cancer Risk

by Hank Dart

A new study out of France highlights another possible reason to avoid eating too many highly processed foods:  They may increase the risk of cancer.

The paper, published yesterday in the British Medical Journal, followed close to 105,000 adults for an average of 5 years.  Along the way, participants were asked to regularly report their dietary intake and any health events, such as a diagnosis of cancer.

Foods were then categorized into groups, with an "ultra-processed" group including foods like: soda (diet or sugary); mass-produced sweets; meats with preservatives other than salt; instant noodles and soups; and foods with industrial food additives and agents.

The proportion of participants' diets that was made up of ultra-processed foods was determined by the weight of food, rather than by calories.  This was done to take into account the potential impact of processed foods that have few, if any, calories, like diet sodas.

The researchers found that for every 10 percent increase in the proportion of ultra-processed foods in the diet, the overall risk of cancer increased by 12 percent and the risk of post-menopausal breast cancer increased by 13 percent.  

Risks were more pronounced when comparing high intake of processed foods with low intake. Participants who ate the most ultra-processed foods had a 21 percent higher risk of cancer overall and a 39 percent higher risk of post-menopausal breast cancer.  They also may have had a higher risk of colorectal cancer, but those results were less reliable.

In the analyses, researchers took into account many factors that could have swayed the results because they could be related to both processed food intake and cancer.  These included factors such as physical activity level, body mass index, alcohol intake, tobacco use, and overall diet quality.

In an accompanying editorial, Adriana Monge of the National Institute of Public Health in Mexico City and Martin Lajous of the T.H. Chan School of Public Health at Harvard University praised the researchers for their detailed study but recommended caution in interpreting such initial results.
"...as with any observational study, confounding by unknown factors common to consumption of ultra-processed foods and cancer outcomes cannot be excluded." 
"Their interesting results require replication and further refinement."
"We are a long way from understanding the full implications of food processing for health and wellbeing."

While more study is needed on the possible links between ultra-processed foods and cancer, well-established dietary recommendations call for limiting certain types of processed foods, which can be high in calories, sodium, refined grains, added sugar, and unhealthy fats -- and low in healthy nutrients.

A largely plant-based diet that is low in unhealthy processed foods and filled with fruits, vegetables, beans, and whole grains is best for overall health and can lower the risk of many important chronic diseases, including cancer.