Recent research published in the journal Cell Report Medicine To compare the impact of a ketogenic diet with reduced free sugar intake on cardiometabolic health.
study: Ketogenic diet, distinct from carbohydrate restriction, alters glucose tolerance, lipid metabolism, peripheral tissue phenotype, and gut microbiota: an RCT. Image credit: Sea Wave / Shutterstock.com
Free sugar restriction
Many modern naturally sweet foods contain free sugars such as glucose and fructose. Limiting free sugars to less than 5% of total energy intake can reduce energy intake by 100 kcal per day.
However, this approach has not been shown to reduce fat mass. A previous study by the present authors found no significant changes in energy balance within 24 hours of ad libitum carbohydrate restriction. This discrepancy may be due to other factors in the energy cycle or inaccurate self-reporting of energy intake.
Carbohydrate restriction
The ketogenic diet reduces carbohydrate intake and alters metabolism to reduce weight, and these effects are due to the production of ketone bodies in the liver as fuel for peripheral tissues.
Previous studies suggest that a ketogenic diet reduces physical activity energy expenditure (PAEE) compared to a high-carbohydrate diet, but it is unclear how the ketogenic diet affects energy cycling and cardiometabolic health.
Energy metabolism in skeletal muscle and adipose tissue can be influenced by physical activity and nutrition, and the gut microbiota producing short-chain fatty acids (SCFAs) also contributes to the regulatory input of these peripheral tissues during fasting and postprandial metabolism.
About the Research
Researchers in the current study randomly selected 60 healthy adults to follow either a ketogenic diet or a low-free-sugar diet for 12 weeks. A third control group was allowed to have a moderate sugar intake.
The ketogenic and low-free sugar groups reported consuming less than 8% and 5% of their total energy as carbohydrates, respectively. In the moderate-carbohydrate group, 18% of their energy was provided by free sugars.
After 12 weeks, study participants in both intervention groups lost fat mass due to reduced energy intake. PAEE did not decrease in either group.
The low free sugar group had reduced total energy intake, total cholesterol, and low-density cholesterol (LDL-C) levels compared to the control group. In the fasting and postprandial states, the respiratory exchange ratio (RER) was reduced in the ketogenic diet group, indicating reduced carbohydrate breakdown for energy.
In the ketogenic diet group, fasting blood glucose levels also decreased by 4 weeks, eventually returning to baseline levels by 12 weeks. Glucose tolerance worsened in this group at both time points.
Lipoproteins, including apolipoprotein B, are responsible for the increased risk of atherosclerosis when cholesterol levels are high. Apolipoprotein B levels increased in the ketogenic diet group, but there were no changes in total cholesterol, LDL cholesterol, or high-density lipoprotein (HDL) cholesterol levels at 12 weeks.
The ketogenic diet group had lower concentrations of amino acids (AA) used for glucose synthesis and higher levels of branched-chain AA, suggesting altered skeletal muscle and adipose tissue metabolism and impaired postprandial glucose uptake by skeletal muscle.
The ketogenic diet group also had higher levels of the inflammatory marker C-reactive protein (CRP) at week 4. Levels of non-esterified fatty acids (NEFAs) were also elevated after the meal, suggesting that lipolysis provides free fatty acids for energy in people following a ketogenic diet.
These changes were not observed by week 12, despite participants continuing to exhibit ketosis throughout the study. Changes in gut microbiota beta diversity were also observed in the ketogenic diet group, Bifidobacteria and Planococcus.
Both restriction groups reported increased cravings for sweet foods by week 12 compared to baseline.
Conclusion
Restriction of free sugars and total carbohydrates reduces energy intake without altering physical activity but has different effects on glucose tolerance, lipoprotein profile, and gut microbiota..”
The findings highlight that low carbohydrate and free sugar intakes maintain PAEE in healthy adults. In contrast, skipping breakfast or alternate-day fasting has been reported to decrease PAEE, possibly due to inadequate energy intake.
Reducing discretionary sugar intake by 1% reduced self-reported energy intake by 14 kcal/day, supporting previous studies, although the reduction in energy intake may be more pronounced with objective measures at approximately 17 kcal/day.
Current studies have shown that these dietary interventions are effective long-term strategies for weight loss, as reduced energy intake resulted in reduced fat and overall body weight. However, only alterations in the gut microbiota and unfavorable metabolic changes at the peripheral and systemic levels were observed with the ketogenic diet. Therefore, reducing free sugar intake may be the optimal dietary approach to obtain cardiometabolic health benefits.
Journal References:
- Hengist, A., Davis, R.G., Wolhin, J., etc (2024) Ketogenic diet, distinct from carbohydrate restriction, alters glucose tolerance, lipid metabolism, peripheral tissue phenotype, and gut microbiota: an RCT. Cell Report Medicine. doi:10.1016/j.xcrm.2024.101667.
