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Should You Try A Low Carbohydrate Diet?

Many people are adopting a so called “low-carb diet” in an attempt to lose weight. Are diets low in carbohydrates – the main source of energy for our bodies – actually safe? 

A diet low in carbohydrates usually allows for non-starchy vegetables like kale, spinach, and peppers. Fantastic; these are powerful nutrient-packed foods. And, sure, it’s wise to avoid refined processed products such as breads and pastries, and many commercial grain-based breakfast cereals which are stripped of intact fibers and minerals. However, a diet low in carbohydrates also means a diet low in whole grains, most fruits, starchy vegetables, beans, and lentils. Once you limit carbohydrates, the remains macronutrients to focus on are fat and protein. The diet usually allows for nuts and avocados, which are high in protein and unsaturated fat – great! – but you may end up getting most of your protein and fat from animal sources, which usually results in too much saturated fat. 

Low carb diets are often designed to deprive the body of glucose for energy and induce a metabolic process called ketosis to burn fat cells. 

Should we really be avoiding so many of the healthiest foods on the planet which are also rich sources of antioxidants, fiber, vitamins, minerals, powerful protein, and phytonutrients? 

Let’s see what the science tells us. 

Noto, et al conducted a review and meta-analysis of studies looking at the effects of low carb diets on cardiovascular disease risk factors. The researchers found low carb diets were associated with a significantly greater risk of all cause mortality.[1] They found that while some studies included in their analysis showed low carb diets were not relevant in terms of cardiovascular disease, subgroup analyses did show low carb diets may increase the risk of CVD and mortality when the diet follows an animal-based pattern and they may decrease such risks in plant-based diet patterns.

Samaha et al found that in morbidly obese individuals (BMI >40), low carb diets induced more short term weight loss than low fat diets.[2] However, the amount of weight lost was small and the study duration was only 6 months. 

Another meta analysis conducted by Bueno, et al studied the effects of a very low carbohydrate ketogenic diet and how it compared to a low-fat diet for long term weight loss. Bueno et al found that very low carbohydrate diets were indeed more effective at reducing body weight, and even increased HDL (good) cholesterol.[3] However, the diet was found to increase levels of LDL (bad) cholesterol levels, which the author points out, was likely due to the diet’s high content of saturated fat. 

In response to this study, researchers in Vienna, Austria conducted a study (also a meta-analysis of randomized controlled trials) to look at the effects of low carb (<45% kcal from CHOs) and low fat (<30% kcal from fat) diets and their effects on endothelial function, a known independent risk factor for atherosclerosis and other markers of cardiovascular disease.[4] This study found that markers of endothelial function were significantly more reduced in those following a low carb diet than in those following low fat diets.

Given the potential for increased mortality, increase in LDL cholesterol, and small amounts of weight loss seen after 6 months may not be a good enough reason to ditch the whole grains, sweet potatoes, and black beans.

After all, people don’t eat carbohydrates – have you ever seen a carbohydrate tree or carbohydrates for sale in the supermarket? No, because people eat foods which contain varying amounts of carbohydrates, amino acids, fats, micronutrients, and phytonutrients, etc. We may be wiser to pay attention to the sources of carbohydrates (think oatmeal versus donuts) and the sources of protein (think black beans versus steak).

Until we have more concrete evidence on the efficacy and safety of low carb diets, let’s focus on what the science says about the effects of high carb diets and disease outcomes.

Citations:

1. 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. doi:10.1371/journal.pone.0055030
2. Samaha F, Iqbal N, Seshadri P, et al (2003) A Low-Carbohydrate as Compared with a Low-Fat Diet in Severe Obesity. New England Journal of Medicine 348:2074-81
3. Bueno, N., De Melo, I., De Oliveira, S., & Da Rocha Ataide, T. (2013). Very-low-carbohydrate ketogenic diet v. Low-fat diet for long-term weight loss: A meta-analysis of randomized controlled trials. British Journal of Nutrition, 110(7), 1178-1187. 
4. Schwingshackl, L., Hoffmann, G. University of Vienna. (2013) Letter to the Editor. Low-carbohydrate dies impair flow-mediated dilation: evidence from a systematic review and meta-analysis. British Journal of Nutrition (2013)