Low Carbohydrate diets, Weight management, Type 2 diabetes and Dyslipidaemia

Low Carbohydrate diets, Weight management, Type 2 diabetes and Dyslipidaemia

Historically, a variety of dietary patterns have been used for weight loss by Health Professionals including the Mediterranean diet, DASH diet, Vegetarian diet, Low fat diet, high protein diet and the Nordic healthy diet to name a few. Recently low carbohydrate and very low carbohydrate diets have been used for weight loss and have particularly been promoted for type 2 diabetes management. It has been shown that the main mode of action of low carbohydrate diets is likely to be due to the reduction in energy intake associated with carbohydrate restriction (1).

What does “low carbohydrate (low-CHO)” mean?

There is lack of clarity on what constitutes the definition of low carbohydrate (2,3). This type of diet can be defined as one containing anything between 20g and 150g carbs per day. Very low-CHO diets- 20-50g CHO daily (emphasising the replacement of CHO with fat) have become popular among lay public as well as some health professionals (4). Typically, there is little emphasis on the type of fat that replaces CHO in such diets, which may result in a high intake of saturated fatty acids and cholesterol. Furthermore, the severe restriction of CHO limits CHO intake to nonstarchy vegetables and eliminates fibre-rich starchy vegetables, as well as most fruits, pulses and wholegrains, which are foods that have been associated with reduced cardiometabolic risk (5)

Low-CHO diets, Weight Loss and Prevention of Type 2 diabetes

Weight loss is the most dominant predictor of  preventing Type 2 diabetes, and it has been demonstrated that weight losses of 5-7% reduce the relative risk of Type 2 diabetes by 50% (6).Every kilogram lost is associated with a 16% relative reduction in risk (7), and losses of 10% may be sufficient to reduce the risk of future Type 2 Diabetes by 80%(8)  .There is strong evidence from RCT s that intensive multicomponent lifestyle interventions incorporating diet and physical activity with sustained weight loss can prevent Type 2 diabetes in high risk individuals from different ethnic backgrounds(9-13). 

A recent review by the National Lipid Association Nutrition and Lifestyle Task Force who examined the current evidence on the effects of low-CHO and very-low CHO diets for the management of body weight and other cardiometabolic factors, concluded that low-CHO and very-low-CHO diets are not superior to other dietary approaches for weight loss in the long term(14). 

Overall evidence suggests that they are safe and effective over the short term for weight loss but the potential adverse effects of such a diet long term on cardiovascular risk remain unknown. Minimal data are available regarding long term (>2 years) efficacy and safety (3).

Findings from observational data has found long-term consumption of extreme CHO intakes (low and high) is associated with all-cause, cardiovascular, and cancer mortality in the general population (14)

Based on the current evidence, the key recommendations for lifestyle interventions to reduce risk of Type 2 diabetes in high risk groups include (16)

  • Where appropriate, aim for weight loss of at least 5%
  • Restrict energy intake to induce 5-7% weight loss
  • Moderate total fat intake (<35% total energy intake)
  • Reduce saturated fat intake to < 10 % total energy intake
  • Increase fibre intake to >15g/1000kcal
  • Increase physical activity, aiming for at least 30 mins/day or 150 mins/week of moderate to vigorous activity
  • Limit alcohol intake to <14 units a week

 Low-CHO Diets and Lipids

It is also important to consider what CHO foods are being replaced with, as this could shift the overall diet to one that impacts other cardiometabolic risk factors. For example, the recent Lipid Association review found that in over-weight and obese individuals, low-CHO and very-low CHO diets had mixed effects on low-density lipoprotein cholesterol (LDL-C) levels, with some studies showing an increase. A high saturated fatty acid (SFA) content was a key factor for the increase in LDL-C (14).

Due to the substantial variation in lipid responses observed in patients choosing to follow low-CHO and very-low-CHO diets, baseline and follow-up lipid profiles should be measured (14).

In terms of other lipids, compared with High Carbohydrate, Low Fat (HCLF) diets, low-CHO diets generally decrease triglyceride (TG) levels and increase HDL-C in the short term. Improvements in TG and HDL-C were achieved at low and moderate CHO intakes versus very-low-CHO intakes, which may result in better long-term adherence (14)

There may be individuals who experience extreme effects of low-CHO and very-low CHO, high fat (VLCHF) due to genetic factors. For example, patients with known hypercholesterolaemia and familial hypercholesterolaemia (FH) may have a genetic predisposition to increased LDL-C levels with VLCHF/ketogenic diets (KD). As such these diets are contraindicated.

VLCHF/KDs are also contraindicated in patients with a history of hypertriglyceridemia associated acute pancreatitis, and severe hypertriglyceridemia.

Low-CHO Diets and Management of Type 2 Diabetes

For overweight or obese adults with Type 2 Diabetes, reducing energy intake to achieve weight loss should be the primary nutritional management strategy (15). As highlighted previously, low-CHO diets can be safe and effective in the short term in managing weight in people with Type 2 diabetes. BUT based on evidence, low-CHO and very-low-CHO diets are not superior to other dietary approaches for weight loss in the long term.

Examining the effect of low-CHO or very-low CHO diets on glycaemic control, medication use and lipids in Type 2 Diabetes, the National Lipid Association Nutrition and Lifestyle Task Force review found:

  • Low-CHO diets do not reduce fasting blood glucose or insulin levels more than HCLF diets in clinical trials
  • Low-CHO diets result in a greater short-term reduction in HbA1c vs HCLF diets, but there were no differences between diets beyond 1 year.
  • Low-CHO diets resulted in a reduction in the use of diabetes medications, and reductions in the use of diabetes medications were achieved at CHO intake levels that do not induce ketosis.
  • The Mediterranean dietary pattern produced improvements in TG, HDL-C, and HbA1c levels in individuals with T2D compared with low -CHO diets

In the last few years there has been a lot of interest regarding remission of Type 2 diabetes for overweight and obese people. This appears to be related to weight loss and Diabetes UK recommend a weight loss of approximately 15 kg as as possible after diagnosis (16). A weight loss of 5% or more significantly improves HbA1c, total cholesterol-C, HDL-C, TG, blood pressure and insulin sensitivity. To maintain these benefits, it’s important the weight loss is sustained.

Evidence suggests that it is the degree of adherence that predicts outcomes rather than type of diet (16). So rather than cutting out nutrients, it is important to focus on the overall dietary pattern to ensure that the diet is balanced for obtaining and maintaining good health and one that reduces the risk of long-term conditions such as heart disease, type 2 diabetes, cancer and many other conditions.

Key Points

Results from meta-analyses suggest that there is not one macronutrient distribution superior for weight loss or for the management of Type 2 Diabetes
Low-CHO and very-low-CHO diets maybe an option for a short-term initial weight loss period (2-6 months) as long-term cardiovascular risk remains unknown
According to findings from observational studies very low-CHO diets are associated with an increased risk of mortality.
The decision about whether a patient should consider following a low-CHO, or very-low-CHO diet, should be made after careful discussion about the risks and benefits, as well as the patient preference. Health professionals should offer a tailored, multicomponent lifestyle intervention choosing from the variety of dietary strategies that is likely to be the most effective for that individual.
Due to the potential increase in LDL-C and inconsistent effects on HbA1c with low-CHO or very-low-CHO diets, close medical supervision is recommended for patients with established Atherosclerotic Cardiovascular Disease who choose to use these diets.
For those following a low-CHO or very-low-CHO diet, advice should be given on replacing carbohydrates with unsaturated fats, avoiding excessive intakes of saturated fat and cholesterol, as well as encouraging the consumption of appropriate vegetables, fruits, nuts, seeds, legumes, and wholegrains within the context of a CHO-restricted diet.
For long-term weight maintenance and cardiovascular health, emphasis should be placed on CHO foods associated with reduced cardiometabolic risk, including vegetables, fruits, wholegrains, and legumes.

Individuals with FH and patients with a history of hypertriglyceridemia associated acute pancreatitis, and severe hypertriglyceridemia should not follow a very-low CHO, high fat diet.



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