Introduction

Diabetes is a group of endocrine diseases characterised by the inability to properly process glucose leading to elevated blood sugar levels.¹ Type I and type II diabetes are the main forms of the disease. Although the symptoms somewhat overlap, the diseases are caused by different mechanisms. Collectively, type I and type II diabetes affect hundreds of millions of people around the world, putting significant strain on healthcare systems. Diabetes is a chronic disorder with no known cure. People with the disease have to meticulously manage their food intake and sometimes inject insulin regularly to prevent serious complications.² A suitable diet is paramount in diabetes management because the amount of carbohydrates we eat directly impacts the amount of sugar in our blood. As a result, low-carbohydrate diets offer a potential strategy to improve blood sugar levels and reduce dependency on insulin. This article explores the effectiveness and safety of low-carbohydrate diets in the context of diabetes management.

What is diabetes?

Diabetes can develop through two main mechanisms, both of which result in incorrect processing of dietary carbohydrates. In type I diabetes, an autoimmune reaction occurs in which the body attacks its own insulin-producing cells (beta cells) in the pancreas. Over time, this leads to a total or near-total lack of insulin production.¹

Type II diabetes develops in a slightly different way. When we ingest foods rich in carbohydrates (for example refined sugars or starches), our bodies respond by releasing insulin from the beta cells mentioned above. Insulin pushes glucose molecules out of the bloodstream where they can cause harm if too abundant and into cells where they can either be used or stored. However, high levels of insulin have another effect: the promotion of fat storage.³ The carbohydrate-insulin model dictates that if a person eats a lot of carbohydrates, the high levels of insulin released will promote fat storage and weight gain over time. Persistent spikes in insulin levels can result in insulin resistance. In this process, the body becomes less sensitive to the effect of insulin, a hallmark of type II diabetes. Because the cells and tissues of the body are less sensitive to insulin, the glucose levels remain high in the blood after a meal and the pancreas releases more insulin in an attempt to lower them. Over time, if this resistance worsens, the person can have consistently high glucose levels in the blood and develop problems over time.

What exactly is a low-carb diet?

A low-carb diet limits carbohydrate intake, expressed as a percentage of total calories.⁴ For example, someone on a 2,000 kcal diet might limit their carb intake to 200 kcal, or 10%. In contrast, a typical low-fat diet includes 55–65% calories from carbohydrates. The definition of low-carb can vary somewhat, from very low (<10%, as in ketogenic diets) to moderate (20%-30%).

Key low-carb foods include:

• Meat, poultry, fish, and seafood
• Low-carb vegetables like leafy greens, broccoli, and peppers
• Nuts and seeds
• Healthy fats
• Dairy such as cheese and unsweetened yoghurt
• Avocados and berries

Foods to avoid on a low-carb diet include:

• High-carb vegetables like potatoes and corn
• Most fruits, except some berries
• Grains and legumes
• Sugary foods and processed snacks
• High-carb dairy products

Why do low-carb diets work for diabetes?

Low-carb diets aim to reduce the impact of dietary intake on blood sugar levels by minimising the consumption of sugars and starches.⁴ When meals are primarily composed of fats and proteins, the resulting blood sugar spikes are substantially blunted compared to those caused by carbohydrate-rich meals. This is because fats and proteins have a lower glycemic index and do not cause rapid rises in blood glucose levels. Consequently, the body requires less insulin to manage glucose in the blood, reducing the strain on insulin-producing cells in the pancreas.

By limiting carbohydrate intake, the body gradually shifts its primary energy source from glucose to stored fats: a metabolic state known as ketosis.⁵ This process not only stabilises blood sugar levels but also improves insulin sensitivity. Improved insulin sensitivity means that cells are better able to respond to insulin, effectively reducing the likelihood of developing insulin resistance, which is a major concern in type II diabetes.

Furthermore, by stabilising blood sugar levels, low-carb diets help to mitigate the risk of both hyperglycaemia (high blood sugar) and hypoglycaemia (low blood sugar), common issues in diabetes management. This stable metabolic environment is particularly beneficial for individuals with type I diabetes, as it can lead to a reduced need for insulin injections. For those with type II diabetes, it may even facilitate a reversal of the disease's progression by restoring the body's natural ability to utilise insulin effectively.

The benefits of a low-carb diet extend beyond glycemic control. Patients often report increased energy levels, better mental clarity, and a reduction in cravings for sweets, all of which contribute to better adherence to the diet and an improved quality of life.

Benefits of a low-carb diet for diabetics

Low-carb diets can potentially benefit those with either type I or type II diabetes, although the reasons are slightly different. In both cases, fewer carbs enter the system and the need for insulin diminishes. In the case of type I diabetes, these reduced glucose inputs will mean that less insulin can be injected. A common long-term effect of type I diabetes is insulin resistance, the hallmark of type II diabetes. In those with type II diabetes, it can be possible to prevent or remove the need to inject insulin if the metabolism returns to a healthy state. There are several studies showing that low-carb diets can improve blood glucose control, which is usually measured using HbA1c, a marker of medium-term blood glucose levels.^6,7

Potential issues and considerations

The advantages of low-carb diets in people with diabetes are fairly well established, but there are downsides and potential risks, ranging from nutrient deficiencies to the risk of ketoacidosis in type 1 diabetes. Many nutrient-rich foods are high in carbohydrates and likely to be omitted from the diet, so it is important to make sure that adequate micronutrients are obtained either through food or supplementation.

Furthermore, although low-carb diets do show solid evidence of efficacy, they are not the only show in town when it comes to diabetes management. Some studies suggest that a Mediterranean diet, which tends to be relatively high in carbohydrates, is just as effective at lowering HbA1c as a low-carb diet overall.⁴ This is an important finding because a Mediterranean diet is inherently more diverse than a typical low-carb diet and can in some cases be more nutritious. The best approach is to try multiple diets with the help of a dietician to discover the best balance for each individual.

For some time, a concern surrounding low-carb diets in diabetes was the potential for elevated low-density lipoprotein cholesterol levels due to increased fat intake. However, multiple studies have largely dispelled this idea, demonstrating that low-carb diets improve most biomarkers for cardiovascular disease, such as hyperglycaemia, hypertension, and atherogenic dyslipidemia.⁸

Practical tips for implementing a low-carb diet

The average person can usually experiment with low-carb diets with few risks. Diabetics should be more careful, and ideally, begin any new diet with help from their healthcare provider. For type I diabetics, one of the main considerations is any adjustments that might be needed for insulin doses. When eating much less carbohydrates than normal, insulin requirements will be drastically reduced. If these adjustments aren’t made properly, the risk of potentially fatal hypoglycemia events is increased.

The best way to follow any specific diet is to plan meals in advance to reduce the temptation to resort to unhealthy last-minute fixes. A dietician should be able to help develop a meal plan that is easy to follow, nutrient-rich, and importantly meets the calorie and macronutrient targets recommended by a healthcare provider.

When changing to a low-carb diet, it’s fairly normal for the usual blood glucose patterns to deviate significantly. For example, morning highs or lows might change. Furthermore, the specific amount of insulin needed for a specific meal might change over time with weight loss and improvements in insulin sensitivity. The best way to keep on top of this is to follow a rigorous blood glucose monitoring regimen. Several technological solutions exist for this, and it is wise to consult with a healthcare provider to decide which method suits your desired lifestyle.

Future perspectives

As the incidence of diabetes is increasing, there is a lot of interest in researching the disease to better understand and treat it. In particular, recent studies are attempting to figure out how different diets affect insulin sensitivity and beta-cell function.⁹ Alongside these dietary studies, new technologies like continuous glucose monitoring and sophisticated mobile app integration are making it easier for people to track their blood sugar levels. Advances in artificial intelligence are helping in meal planning and correct adjustment of insulin doses for those injecting or using pumps. There is also great promise in the development of the so-called ‘artificial pancreas’ which couples a sensitive real-time glucose monitor with a pump to essentially remove some of the lifestyle impact of monitoring levels and administering insulin.

Summary

Diabetes is a chronic disease affecting the body's ability to properly process glucose, leading to spikes in blood sugar levels. The two types of diabetes are type I and type II, both types having different mechanisms by which they affect the body. It is suggested that a low-carb diet can help manage the symptoms associated with both types of diabetes, as it diminishes the body's need for insulin, reduces the risk of hypoglycaemia and hyperglycaemia, and leads to the body going into the metabolic state of ketosis. However, this is something that must be done after consulting with a healthcare provider as it comes with certain risks and precautions, one of the risks being a chance of developing ketoacidosis.