Carbohydrate-restricted dietary patterns have recently gained popularity for weight loss as well as the management of type 2 diabetes (T2D). In addition, recent research has highlighted the improvement in several cardiometabolic risk factors such as hemoglobin A1c (HbA1c), high-density lipoprotein cholesterol (HDL-C), and triglyceride (TG) in people who follow a carbohydrate-restricted dietary pattern. However, it is not clear how low people must go concerning restriction of carbohydrate intake as well as the duration to balance the benefits and harmful effects.
A new review in the Journal of Clinical Lipidology aimed to describe the definitions of carbohydrate-restricted dietary patterns, the potential benefits related to cardiometabolic risk factors, and whether healthcare professionals should consider it for glycemic management and weight loss.
Editorial: How low should one go in reducing carbohydrate? Image Credit: sulit.photos / Shutterstock
What are carbohydrate-restricted dietary patterns?
Published literature so far does not include accurate definitions for carbohydrate-restricted dietary patterns. According to research reviewed by the American Diabetes Association for their 2022 Standards of Care, less than 26 percent of total daily energy (TDE) was considered a low-carbohydrate dietary pattern. Another research indicated less than or equal to 10 percent TDE to be very low-carbohydrate, 11 to less than or equal to 25 percent to be low-carbohydrate, and less than 45 percent to be moderate carbohydrate diets.
In order to achieve ketosis, patients are advised to restrict carbohydrate intake to less than 10 percent TDE, as well as protein intake to a moderate level.
Carbohydrate-restricted dietary patterns, weight loss, and glycemic control
Several studies have indicated carbohydrate-restricted dietary patterns to be associated with a decrease in body weight up to 6 months, but no difference was observed at 12 months. Another dose-response meta-analysis also reported the most significant reduction in body weight to take place for people at a carbohydrate intake of 35 percent TDE at 12 months, but no reduction took place beyond 12 months as compared to people with higher carbohydrate intake. However, no significant difference regarding fasting blood glucose (FBG) was observed between the low-carbohydrate and high-carbohydrate diet groups.
HbA1c levels were observed to be lower in the short term but not beyond 12 months in adults with T2D or obesity. Moreover, a reduction in body weight due to carbohydrate-restricted dietary patterns will help improve insulin sensitivity, improving HbA1c levels. Studies have also indicated a reduction in the need for diabetes medications on intake of carbohydrate-restricted diet. The duration of the diet must be as long as a person can maintain it long-term. However, most studies do not support the very low-carbohydrate diet. Instead, they indicate that moderate carbohydrate intake can achieve clinically significant benefits. Moderate carbohydrate diets have been reported to improve HbA1c and TG levels and increase long-term adherence compared to diets with more severe restrictions.
However, people prescribed sodium-glucose cotransporter 2 (SGLT2) inhibitors must be careful since these inhibitors modulate the transportation of glucose through the kidney and inhibit renal glucose reabsorption. They also produce low-grade ketosis. Therefore, people taking SGLT2 inhibitors must avoid ketogenic diets and very low-carbohydrate diets due to the risk of euglycemic ketoacidosis.
Concerns regarding carbohydrate-restricted dietary patterns
One main concern regarding the degree of carbohydrate restriction essential for the production and maintenance of ketosis as well as less severe carbohydrate restriction, is an increase in atherogenic lipoprotein levels, as highlighted by the increase in apolipoprotein B (Apo B) and LDL-C concentrations. LDL-C has been reported to decrease during periods of negative energy balance, which is required for weight loss. Few studies have reported an increase in LDL-C levels on consuming a low-carbohydrate diet. An increase in LDL-C has been reported to occur due to the replacement of carbohydrate-rich foods with foods high in cholesterol and saturated fatty acids. Therefore, people following a carbohydrate-restricted dietary pattern must consume foods high in unsaturated fatty acids and limit food high in cholesterol and saturated fatty acids to reduce adverse changes in lipoprotein lipids and lipoproteins.
Components of healthy dietary patterns
Dietary patterns associated with low cardiometabolic disease risk must include whole grains, seeds, nuts, vegetables, fruits, non-tropical oils, legumes (pulses), and lean protein sources. Such dietary patterns are low in cholesterol, saturated fats, and sodium in comparison to the typical diet of the US. Cardioprotective dietary patterns must also contain high levels of components with putative health benefits, which involve phytochemicals, magnesium, potassium, and dietary fiber. Therefore, while carbohydrate-restricted diets are helpful for glycemic control and weight loss, healthcare professionals must also encourage the transition to dietary patterns associated with longer-term favorable health outcomes.
Extreme intake of carbohydrates and mortality
Extreme consumption of carbohydrates can lead to adverse health outcomes. Previous observational studies have indicated that very low- and very-high-carbohydrate intake has been associated with all-cause, cancer, and cardiovascular-related mortality. Another study reported that diets with low and high carbohydrates were associated with higher mortality compared to about 50 percent TDE consumption from carbohydrates. Therefore, the Institute of Medicine has recommended the acceptable macronutrient distribution range (AMDR) to be 45-65 percent TDE from carbohydrates. Although some people can achieve and maintain a carbohydrate-restricted dietary pattern with less than 40 percent TDE for long periods, it might make consuming foods that contain adequate nutrients and non-nutrient dietary components associated with favorable cardiometabolic health outcomes difficult.
Importance of the quality of foods in healthy dietary patterns
Healthcare professionals must give importance to the overall quality of the food as compared to only the quantity of macronutrients. This will help to increase the intake of nutrient-dense foods that provide high-quality protein, carbohydrate, fat, fiber, micronutrients, and bioactive compounds. Healthy dietary patterns with high-quality foods have been reported to be associated with a 10 to 20 percent lower risk of cardiovascular disease (CVD) as well as CVD-associated mortality. Higher-quality dietary patterns include consuming nutrient-dense foods with minimal processing, such as whole grains, fresh fruits, and vegetables, as well as lean sources of animal proteins.
Previous research has highlighted that consumption of whole grains, fruits, and pulses has led to improvement in cardiometabolic risk factors as well as decreased risk of T2D, CVD, and CVD mortality. One recent review suggested that a dietary pattern can promote cardiometabolic health by comprising high-quality carbohydrate foods, irrespective of high or low TDE. The recently completed Keto-Med Diet crossover clinical trial is an example of the benefit of high-quality carbohydrate-rich foods within carbohydrate-restricted dietary patterns.
Recommended healthy dietary patterns examples
Recommended healthy dietary patterns involve the vegetarian, Mediterranean, and Healthy US patterns, which consist of at least 45 percent TDE from carbohydrates. Modifying the recommended healthy dietary patterns can lower carbohydrates for people wanting to consume fewer carbohydrates. As a result, people can consume about 40 percent TDE carbohydrates and still eat healthily.
The Mediterranean dietary pattern has been reported to have the most robust scientific evidence concerning reduced cardiometabolic disease risk. Many studies have reported the Mediterranean dietary pattern to improve HDL-C and TG levels along with HbA1c for patients with T2D. A traditional Mediterranean dietary pattern (CORDIOPREV) or a Mediterranean dietary pattern supplemented with extra-virgin olive oil or mixed nuts(PREDIMED) have also been reported to reduce CVD risk. The cardiovascular benefits in both these diets were observed to be achieved with a carbohydrate intake lower than the AMDR.
People choosing to follow a carbohydrate-restricted dietary pattern must find a replacement for foods rich in cholesterol and saturated fatty acids. People’s preferences, health status, and other factors impact their ability to follow and maintain dietary patterns successfully. Individualized medical nutrition therapy and lifestyle counseling can be provided by registered dietitian nutritionists (RDNs) to educate people about the dietary pattern that will fit them best, along with encouraging the consumption of foods rich in unsaturated fats and high-quality carbohydrate foods.
The study indicates that people must follow a dietary pattern that contains at least 40 percent TDE for long-term consumption. Healthcare professionals must emphasize the consumption of high-quality foods with minimal processing. Several recommended dietary patterns are available, with the Mediterranean being the most effective in improving cardiovascular outcomes and decreasing T2D incidence. People must consult an RDN to determine which dietary pattern would be most suitable for them and for how long, considering their cardiometabolic risk factors and overall health.