Low Fat or Low Carb, What Science Says?
Diet is central to healthy living but what diet is best for you? To answer this we will look at the role of two macronutrients carbohydrates and fat in weight loss and general health outcomes known as "all cause mortality".
There is no dispute about the significant contribution of obesity (excess body weight) to disease and subsequently reduction in life expectancy. For instance, cardiovascular disease is the leading cause of mortality (death) globally with excess body weight as one of the major risk factors.
Masters et al. showed a significant relationship between all grades of obesity and increase mortality (Masters et al., 2013). Further studies also revealed a relationship between grades of obesity and all-cause mortality rates even after factors such as age, gender, ethnicity and education were factored in. (Borrell & Samuel, 2014).
So to simplify we can use body weight (and or weight loss) as a predictor of overall health. Both carbohydrate and fat can play significant role in weight gain and reduction.
Let's look at which of these two macronutrient are more important (low fat or low carb).
Low Fat or Low Carb For Weight Loss
So the question for most people with obesity or increased weight is what is the most efficient way to reduce your weight?
Of coarse, which diet (low fat or low carb) is more important in achieving weight loss and reduced risk of mortality is an area of debate. Weight gain results from positive energy balance (more energy than what the body requires). This excess energy is often converted to fat.
Traditionally speaking it was thought that a low fat diet was superior since one gram of fat gives higher energy as compared to a gram of carbohydrate (9kcal vs. 4kcal). This wisdom is being called into question recently.
For instance several studies have shown that reducing carbohydrates (past a certain threshold) in your diet will lead to an increase in fat metabolism and breakdown even when calories stay the same. Fat breakdown is known as beta oxidation and translates into weight loss. However not all research shows higher weight loss in those on low carb compared to low fat. In fact a recent study looking at obese but non-diabetic individuals lost more weight on higher carbohydrate and lower fat diet.
What is going on?
What appears to be the common denominator is the efficiency of glucose (aka carbs) metabolism. A study by Hjorth et al., 2017 showed that the ability of overweight individuals to loose weight on a given diet could be predicted by their ability to metabolize carbohydrates. So if you have normal glucose control, a low fat diet will likely be better. If you don't have normal glucose control/ metabolism, you will likely loose weight easier on lower carbohydrate higher fat diet.
What is also interesting is that some people have more of a challenge metabolizing certain types of dietary fat for genetic reasons. If this were factored in to the study above, the low carb result may have been even more pronounced.
Another important factor to note is how we define "normal" glucose metabolism.
Low Fat or Low Carb for Cardiovascular Disease
Studies have also shown that although low carbohydrate and low fat diet are both beneficial in achieving weight loss. Patients placed on the former have lower cardiovascular risk.
Specifically the lower carb diet tends to create a greater reduction in total cholesterol and low density lipoprotein and create a greater increase in high density lipoprotein. All of these provide a superior reduction in cardiovascular risk (Hu et al., 2012).
However, Fung et al. in 2010 found a lower all-cause mortality in those with plant based low carbohydrate diets but higher all-cause mortality in patients with animal based low-carbohydrate diet. These findings are interesting and noteworthy especially since this study was on healthy individuals without cardiovascular disease or diabetes.
Remember that those with elevated blood sugar, benefit the most from lower carbohydrates diet. It is also interesting to see the animal based low carb did not reduce risk and potentially raised risk. This likely stems from the fact that most people that are consuming a low carbohydrate diet tend to consume higher amounts of animal proteins. This research should provide caution against higher animal proteins at the expense of carbohydrates.
Unless, that is, you have diabetes.
What Diet Should You Follow?
Follow your specific risks. Look at your genetics or family history and pinpoint where there is more risk. If you have a lot of cardiovascular disease in your family follow, a diet that reduces cardiovascular risk (typically low carb) will lily be beneficial. With this lower carbohydrate diet. If you are more cancer prone, then limiting animal protein will be beneficial. A lower carbohydrate (ketogenic diet) diet may still be beneficial for those with higher cancer risks but consumption of animal protein should be more limited and controlled.
Since cardiovascular disease is the leading cause of death globally and obesity is a major risk factor, a low carbohydrate appears to have more benefit for most people.
Keep in mind that this type of diet is probably going to benefit those with higher risk for cardiovascular disease, diabetes, and blood sugar dysfunction. While we did not get into the specifics of each diet that was researched a low carbohydrate diet can be loosely defined as a diet that derives less than 20% of calories from carbohydrates.
To get a customized diet plan for your health come in for a visit or to learn more a free consultation.
1. Borrell, L. N., & Samuel, L. (2014). Body Mass Index Categories and Mortality Risk in US Adults: The Effect of Overweight and Obesity on Advancing Death. American Journal of Public Health, 104(3), 512-519. doi:10.2105/ajph.2013.301597
2. Fung, T. T., van Dam, R. M., Hankinson, S. E., Stampfer, M., Willett, W. C., & Hu, F. B. (2010). Low-carbohydrate diets and all-cause and cause-specific mortality: Two cohort Studies. Annals of Internal Medicine, 153(5), 289–298. http://doi.org/10.1059/0003-4819-153-5-201009070-00003
3. Hu, T., Mills, K. T., Yao, L., Demanelis, K., Eloustaz, M., Yancy, W. S., … Bazzano, L. A. (2012). Effects of Low-Carbohydrate Diets Versus Low-Fat Diets on Metabolic Risk Factors: A Meta-Analysis of Randomized Controlled Clinical Trials. American Journal of Epidemiology, 176(Suppl 7), S44–S54. http://doi.org/10.1093/aje/kws264
4. Masters, R. K., Reither, E. N., Powers, D. A., Yang, Y. C., Burger, A. E., & Link, B. G. (2013). The Impact of Obesity on US Mortality Levels: The Importance of Age and Cohort Factors in Population Estimates. American Journal of Public Health, 103(10), 1895-1901. doi:10.2105/ajph.2013.301379
5. Noto, H., Goto, A., Tsujimoto, T., & Noda, M. (2013). Low-Carbohydrate Diets and All-Cause Mortality: A Systematic Review and Meta-Analysis of Observational Studies. PLoS ONE, 8(1), e55030. http://doi.org/10.1371/journal.pone.0055030