Study under review: Calorie for Calorie, Dietary Fat Restriction Results in More Body Fat Loss than Carbohydrate Restriction in People with Obesity
Some of you may have already come across our blog post about this recent blockbuster of a paper published by Dr. Kevin Hall et al. If you have, stick around for our extended F.A.Q. section where we tackle the numerous questions brought up about the study. If you haven’t read the blog, let’s dive right into the trial analysis.
For some, the central dogma behind the hypothetical superiority of low-carb diets for fat loss is the insulin hypothesis of obesity. Part of this hypothesis states that by restricting carbohydrates you will see a stepwise decrease in insulin secretions. Because insulin plays a part in the regulation of fat storage, it has been theorized that the less insulin secreted the more free fatty acids will be released from adipose stores leading to increased fat oxidation and rapid fat loss. These assumptions have led to the idea that low-carb diets will induce greater fat loss over a low-fat diet even when calories are held constant. Gary Taubes, an advocate of the low-carb approach, posited the following in his latest book, Why We Get Fat (p. 144-47):
Simply put, Taubes suggests that by reducing both carbs and fat in low-fat diets it is possible that reductions in carbohydrate intake could be responsible for any fat loss seen. Taubes is correct in that researchers who run diet trials often alter the amount of fat and carbohydrate participates eat, making it impossible to determine if restricting one will lead to greater fat loss over the other. Previous studies on low-fat and low-carb diets have changed multiple variables simultaneously. So even though they end up comparing low-fat and low-carb, they do not specifically reduce one macronutrient or the other from a baseline diet without changing other variables. In the present study, Dr. Hall and his team set out to eliminate that confounding variable by subtracting either fat or carbs from the diet without changing anything else. This was done under tightly controlled conditions, to determine if indeed there is a metabolic fat loss advantage to going low-carb.
One important concept to understand before reading through this breakdown is that the study was not looking at the real-world efficacy of diet interventions. That is to say, this was not a free living low-fat vs. low-carb study where researchers educate groups of volunteers and let them eat self-directed low-fat or low-carb diets in their own homes to see how they fare. The investigators designed this intervention to examine some specific mechanisms of weight loss discussed in the sections below.
One version of the insulin hypothesis states that in order to lose body fat you must restrict carbs to bring down insulin, high levels of which will prevent fat loss. Dr. Hall’s study has been designed to test this hypothesis to see if reduced-carb diets confer a fat loss advantage over reduced-fat diets when calorie intake is strictly controlled.
Other Articles in Issue #11 (September 2015)
A shot to the gut
Alcohol intake and gut impacts have been researched before, but we still aren’t sure what exactly goes on after people drink. This study looked at what happens with gut bacterial products when people have multiple drinks at one sitting ... aka “binge drinking”.
Tea time means only tea for optimal EGCG absorption
Many people drink green tea for health, and some take green tea or EGCG supplements in an attempt to shed extra fat. While these topics have been researched at length, there hasn’t been as much research on timing. This study looks at EGCG absorption with and without food.
Can omega-3s prevent cognitive decline?
One of the most important issues with aging is decreased cognitive ability and eventually dementia. Since the brain has such high omega-3 content, many people supplement for prevention of these issues. This large, multi-year study put that practice to the test.
- Interview: Dylan Dahlquist, MSc(c)
When is breakfast the most important meal of the day?
With an increasing amount of research pointing to benefits of intermittent fasting, breakfast has been shunned by more and more people. But for those with type 2 diabetes, blood sugar is a central issue, and breakfast may play a major role in regulating it.
What to Expect When We’re Expecting: Fetal Programming and the Development of Taste Preferences
. By Margaret Leitch, Ph.D.
Gluten-intolerant? There’s a pill for that
Some people are lactose intolerant, but still drink milk thanks to the availability of lactase enzymes. That setup isn’t yet possible for those who don’t handle gluten well. This study examines the efficacy of a promising enzymatic adjunct to a gluten-free diet.
Vitamin D(efense) against Crohn’s disease?
Immune benefits are often listed among the multitude of possible vitamin D effects. Most of the time, this is simplified to “defense against colds and flu”. But many conditions have an immune component — this particular study examines potential mechanisms by which vitamin D may help Crohn’s disease.
Green tea: a potential pain in the neck
Though it may not be as effective for fat loss as early studies suggested, green tea is still seen as extremely healthy. But animal evidence has pointed to possible thyroid side effects from excessive green tea consumption. How convincing is this evidence?