The Great Debate: Carbs vs. Fat

 

Submitted by Amy Sercel MS RD CD

Edited by Marcia Bristow MS RDN CSSD CD

A few weeks ago, the media yet again caught onto a new nutrition study.  You might have heard about it in an article titled something like “Large diet study suggests it’s carbs, not fats, that are bad for your health,”¹ “New study favors fats over carbs,”² or even, “Large-scale dietary study: fats good, carbs bad.”³ Many of these articles dramatically over-simplify the original research.

The study analyzed the diets of 135,335 people living in 18 different countries, then followed these people for an average of 7 years to track their health outcomes.  After seven years, the researchers compared participants’ original dietary patterns to their risks of dying from any cause, developing cardiovascular disease, and dying from cardiovascular disease during the time of the study. 

Researchers found that the risk of dying from any cause increased as people ate more carbohydrates.  Specifically, when carbohydrates made up about 77% of a person’s total calorie intake, they were 12-22% more likely to die during the study than when carbohydrates made up about 46% of total calorie intake.⁴ Right now, it’s recommended that 45-65% of your calories come from carbohydrates

On the other hand, people who consumed an average of 35% of their calories from fat had a 5-10% lower risk of death, heart disease, stroke, or heart attack than people who only consumed about 10% of their calories from fat.  Furthermore, people with higher intakes of saturated fat were not any more likely to develop heart disease, have a heart attack, or die from a heart attack.⁴ The highest intake of saturated fat was around 12% of total calories.  The current recommendations suggest that 20-35% of calories come from all types of fat, and no more than 10% of calories come saturated fat.

It’s interesting to compare the original research to the articles published in the media.  These articles seem to promote the idea that all carbohydrates are “bad.”  This may lead you to believe you should stop eating carbohydrates altogether and eat more of all types of fat.  In reality, the original research article does not recommend doing so.  The researchers did not find any health benefit when carbohydrate intake was less than 50% of calories.⁴

Furthermore, carbohydrates come from a wide variety of foods.  While it’s true that foods like candy, soda, and refined flour are all sources of carbohydrates, you also get carbohydrates from fruits, vegetables, dairy products, beans, nuts, and whole grains.  These foods provide important vitamins and minerals, as well as fiber and antioxidants that have been shown to protect against certain diseases.

There are several limitations to this study that make it difficult to draw conclusions that apply to the average person’s diet.  Most significantly, the researchers did not differentiate between the sources of participants’ carbohydrates, and the authors admit that the countries with the highest carbohydrate intakes tend to eat large quantities of white rice and white bread.⁴ It’s already known that eating a diet high in refined carbohydrates and sugar elevates your blood sugar and may lead to insulin resistance, which in turn can cause your liver to secrete more triglycerides into your blood because your cells aren’t getting the energy they need from carbohydrates.  As a result, you may be more likely to develop cardiovascular disease if your sugar intake is high.⁵

At the same time, peoples’ needs for carbohydrates, protein, and fat vary significantly based on their lifestyle and activity levels.  For example, endurance athletes may need up to 70% of their calories to come from carbohydrates to make sure that their muscles have enough fuel to keep them going during an athletic event.  This is important for athletes, but would not necessarily be healthy for someone who is less active.  More follow-up studies are needed to confirm this study’s findings before any of the current nutritional recommendations can be modified.   

Rather than changing your diet based on one research study, meet with a Registered Dietitian who can provide you with individualized, evidence-based recommendations based on your unique lifestyle and needs.  Reduce your intake of refined carbohydrates like white flour and foods high in sugar, and make an effort to choose whole grains, fruits, vegetables, beans, lean protein, and unsaturated fats whenever possible.  These general recommendations have stood the test of time and are not going to change based on one research study.

References:

1.         Large diet study suggests it’s carbs, not fats, that are bad for your health - CBS News. https://www.cbsnews.com/news/large-study-suggests-carbs-not-fats-bad-for-you/. Accessed September 12, 2017.

2.         Bakalar N. New Study Favors Fat Over Carbs. The New York Times. https://www.nytimes.com/2017/09/08/well/new-study-favors-fat-over-carbs.html. Published September 8, 2017. Accessed September 12, 2017.

3.         Large-Scale Dietary Study: Fats Good, Carbs Bad - Slashdot. https://science.slashdot.org/story/17/08/30/0444248/large-scale-dietary-study-fats-good-carbs-bad. Accessed September 12, 2017.

4.         Dehghan M, Mente A, Zhang X, et al. Associations of fats and carbohydrate intake with cardiovascular disease and mortality in 18 countries from five continents (PURE): a prospective cohort study. The Lancet. August 2017. doi:10.1016/S0140-6736(17)32252-3.

5.         Insulin Resistance and Lipid Disorders. Medscape. http://www.medscape.com/viewarticle/584885. Accessed September 12, 2017.