Carbohydrate restriction and low-carb diets have gained popularity in the general population and in research circles in recent years. It shows promise for outcomes such as weight loss and improving diabetes, but there are concerns about the high saturated fat content.
This raises the question – how does a low carb diet affect cardiovascular health markers, particularly after weight loss?
Background
Previous studies on carbohydrate restriction have shown countless potential benefits including weight loss and management of diabetes.
However, the standard dietary guidelines across the globe state that saturated fat content must be reduced to avoid an increased risk of cardiovascular disease and death. This is because studies show saturated fat increases plasma LDL cholesterol, one of the major risk factors for heart disease.
But what this doesn’t consider is other major risk factors for heart disease, including insulin-resistant dyslipoproteinaemia. This is an imbalance in the cholesterol levels induced by insulin resistance. A low carbohydrate diet could reduce this significant risk by reducing insulin resistance.
To investigate the effect on these different cardiovascular health markers, researchers designed a study comparing low, moderate and high carbohydrate diets with different levels of saturated fat.
The study
This study was a secondary study to the Framingham State Food Study. It included participants were aged 18-65 with a BMI ≥25, but excluded those with known cardiovascular disease or diabetes.
During a run-in phase, participants lost 10-14% of body weight over 9-10 weeks on a hypocaloric diet. From here, they were randomly assigned to one of three groups:
- Low-Carb – 20% carb, 60% fat, 20% protein
- Moderate-Carb – 40% carb, 40% fat, 30% protein
- High-Carb – 60% carb, 20% fat, 20% protein
All groups were prescribed 35% of their fat intake as saturated fat, amounting to 21% of total energy for Low-Carb, 14% for Moderate-Carb and 7% for High-Carb.
Along with the anthropometric and various metabolic markers from the original study, the researchers calculated the lipoprotein insulin resistance (LPIR) score. This score is calculated using 6 metabolic markers and the is associated with type 2 diabetes and heart disease.
The findings
LPIR score reduced in the Low-Carb group, remained the same in the Moderate-Carb group, and saw a non-significant increase in the High-Carb group.
The Low-Carb group had fewer large and very large triglyceride-rich lipoprotein particle and higher large HDL particle diameters. It also reduced lipoprotein (a), a major causal risk factor for atherosclerosis.
LDL, LDL particle diameter and inflammatory markers did not differ between the groups.
Conclusions
The researchers concluded that a low-carbohydrate, high saturated fat diet improved insulin-resistanct dyslipoproteinaemia and lipoprotein (a) without causing any adverse effect on LDL cholesterol.
Furthermore, it was found that carbohydrate restriction may lower cardiovascular disease risk independent of body weight changes, which is an exciting possibility that requires further research.
The major limitation noted was the inability to generalise to larger populations. The participants were young to middle aged, relatively healthy and had lower LDL cholesterol. More research would be required to see how it could apply to older, high risk groups or those on a more restrictive ketogenic diet.
They also noted that even with macronutrient targets, diets can differ in terms of fat ratios, glycaemic index, micronutrient content, fibre intake and food processing. These could further influence the outcome.
Reference
Ebbeling, C.B., Knapp, A., Johnson, A., Wong, J.M., Greco, K.F., Ma, C., Mora, S. and Ludwig, D.S., 2021. Effects of a low-carbohydrate diet on insulin-resistant dyslipoproteinemia—a randomized controlled feeding trial. The American Journal of Clinical Nutrition.