Does a Low-Carb Diet Increase Insulin Resistance or Impact Sensitivity?

Part 2: ‘It’s important to know that low-carb diets don’t always mean less insulin. Low-carb diets frequently increase insulin resistance.’

As a follow up to our previous blog article related to a question by a concerned mom who was told by her medical team that ‘It’s important to know that low-carb diets don’t always mean less insulin. Low-carb diets frequently increase insulin resistance.’, today, we will dissect the statement made by the medical team and answer whether:

‘Low-carb diets frequently increase insulin resistance.’

The assertion that low-carb diets “frequently increase insulin resistance” is misleading and not supported by the bulk of the evidence. In fact, a reduction in carbohydrate intake typically improves insulin sensitivity.

The confusion often arises from a temporary physiological response known as "physiological insulin resistance" or "adaptive glucose sparing," which is sometimes observed in individuals following a low-carb or ketogenic diet.

Physiological Insulin Resistance: This phenomenon occurs when the body switches its primary fuel source from glucose to fat (or ketones). In this state, the body becomes very efficient at using fat for energy and reduces its reliance on glucose. As a result, muscle cells may temporarily resist taking up glucose. This isn’t the same as pathological insulin resistance, which is harmful and associated with metabolic diseases like Type 2 diabetes.

In physiological insulin resistance, the body is merely conserving glucose for tissues that need it most, like the brain and red blood cells. This adaptation helps maintain overall energy balance when carbohydrates are restricted. Importantly, this is not harmful and resolves quickly when carbohydrates are reintroduced into the diet.

Insulin Sensitivity and Low-Carb Diets

In contrast to the idea that low-carb diets increase insulin resistance, research consistently shows that low-carb diets enhance insulin sensitivity in many contexts, particularly in people with Type 1 diabetes or those with insulin resistance. As illustrated by the various studies in our previous post:

• Neuman et al. (2024): This study demonstrated that children and young people with Type 1 diabetes who followed a low-carb diet significantly reduced their insulin needs, suggesting improved insulin sensitivity.
• Lennerz et al. (2018): This study found that individuals on a very low-carb diet reduced their insulin doses by 30% while maintaining excellent glycemic control, indicating that lowering carbohydrate intake can reduce insulin requirements without harming insulin sensitivity.
• Turton et al. (2018): After implementing a low-carb diet, insulin needs dropped by an average of 27%, reinforcing the idea that reducing carbs can improve insulin sensitivity and blood glucose control.

These studies show that reducing carbohydrate intake directly reduces the amount of insulin required to control blood glucose levels, suggesting that insulin sensitivity—not resistance—is typically impacted by low-carb diets, and in a positive direction.

When Could a Low-Carb Diet Appear to Increase Insulin Resistance?

There are situations where people might observe what seems like increased insulin resistance when following a low-carb diet. However, this is not due to the reduction of carbohydrates but can be related to other factors, such as:

1. High Dietary Fat Intake: Many low-carb diets, especially ketogenic diets, are high in dietary fat. Research shows that a high intake fat can impair insulin sensitivity, particularly if the diet is very high in fat and low in fiber. Studies like those by Hernandez et al. (2017) and Boden et al. (2005) show that excess fat can disrupt insulin’s ability to signal to cells, leading to reduced glucose uptake.

2. Free Fatty Acid Release: When fat consumption is high, the body releases free fatty acids into the bloodstream, which can contribute to insulin resistance by interfering with insulin signaling pathways in muscle and liver cells. Dresner et al. (1998) and Roden et al. (1996) discuss how elevated free fatty acids are linked to decreased insulin sensitivity.

3. Imbalanced Macronutrient Ratios: While reducing carbohydrates helps stabilize blood sugar, if a low-carb diet is unbalanced, with too much fat and too little protein, this could potentially impair insulin sensitivity over time. 

Thus, any appearance of increased insulin resistance on a low-carb diet is attributable to high fat intake, rather than the reduction of carbohydrates itself.

However, Westman (2005) in a study titled "Insulin Resistance from a Low-Carbohydrate, High-Fat Diet Perspective", the researchers examined the effects of low-carbohydrate, high-fat diets on insulin resistance and sensitivity, primarily in the context of individuals with metabolic conditions like obesity and diabetes.

The study asserted that low-carbohydrate, high-fat (LCHF) diets do not inherently increase insulin resistance. In fact, the researchers argued that the reduction of carbohydrates in the diet tends to improve insulin sensitivity due to lower blood glucose levels and reduced insulin demand. The study suggested that dietary fat, especially when combined with low-carbohydrate intake, might not have the same negative effect on insulin sensitivity as it would in high-carbohydrate diets.

The conclusion of the Westman study was that insulin sensitivity improves on low-carbohydrate diets, despite high fat intake. This improvement is attributed to the fact that reducing carbohydrate consumption decreases the need for insulin and allows the body to maintain more stable blood glucose levels. The study indicated that the combination of high-fat and low-carbohydrate intake, in the absence of high levels of dietary carbohydrates, does not lead to the kind of insulin resistance typically seen in high-carbohydrate, high-fat diets.

Essentially, the study highlighted that it is the combination of high carbohydrates and high fats that tends to impair insulin sensitivity, rather than dietary fat itself. In a low-carb context, the body utilizes fat as a primary fuel source, leading to better metabolic outcomes without necessarily increasing insulin resistance.

Low-Carb Diets: Different Approaches for Different Conditions

It is important to distinguish between different types of low-carb diets, as not all low-carb diets are the same. In the medical community, there is sometimes confusion between the low-carb, high-fat ketogenic diets used to treat epilepsy and the low-carb, high-protein approaches used for managing Type 1 diabetes.

The classic ketogenic diet used to manage epilepsy is a strict high-fat, low-carb approach (often a 4:1 or 3:1 ratio of fats to carbohydrates and protein). This specific nutrition therapy is designed to reduce seizure frequency by inducing a state of ketosis. However, this type of diet is not ideal for managing Type 1 diabetes because its focus on high fat intake which can negatively impact insulin sensitivity.

In contrast, a Therapeutic Carbohydrate Reduction (TCR) strategy for Type 1 diabetes is focused on low-carb, high-protein nutrition. This approach prioritizes protein for growth and muscle maintenance while reducing carbohydrates to stabilize blood glucose. The goal is not ketosis, but rather to safely achieve normal, stable blood glucose levels.

• Bell et al. (2015) explored the effects of dietary composition on glycemic control in Type 1 diabetes, showing that high-protein, low-carb meals result in better blood glucose outcomes without inducing the issues seen with high-fat ketogenic diets. This underscores the need to tailor the nutritional approach to the specific medical condition.

The key takeaway here is that while both ketogenic diets for epilepsy and TCR for Type 1 diabetes reduce carbohydrate intake, they are not the same nutrition therapy. Medical professionals should have a solid understanding of the differences between these strategies to recommend the correct approach for each condition.

Why Might Someone with Type 1 Diabetes Require More Insulin After a Low-Carb, High-Fat Meal?

It’s not unusual for people with Type 1 diabetes to find that high-fat meals require more insulin, even if the carbohydrate content is low. This phenomenon is due to the metabolic effects of dietary fat.

Fat Delays Digestion and Increases Insulin Resistance Temporarily: Fat slows down the digestion of carbohydrates, leading to a delayed postprandial (after-meal) blood sugar rise. This can require additional insulin doses hours after the meal to control the late blood sugar rise. Moreover, high fat intake can temporarily reduce insulin sensitivity, meaning the body needs more insulin to clear the same amount of glucose from the bloodstream.

Studies like Wolpert et al. (2013) confirm this by showing that when individuals with Type 1 diabetes consume meals high in fat, their insulin requirements increase significantly due to the delayed and prolonged glycemic response. This doesn’t mean they are developing chronic insulin resistance, but rather that fat is influencing insulin’s immediate effectiveness.

Conclusion: Debunking the Myth

The notion that “low-carb diets frequently increase insulin resistance” is inaccurate. Reducing carbohydrate intake does not cause insulin resistance. Instead, a low-carb diet typically improves insulin sensitivity, as carbohydrates are the primary driver of blood glucose spikes and therefore insulin needs.

The real concern lies in the composition of a low-carb diet, particularly the type and amount of dietary fat. A diet excessively high in fat, for example, can contribute to a reduction in insulin sensitivity, and a delay in gastric emptying.

References (APA 6):

Bell, K. J., Gray, R., Munns, D., Petocz, P., & Howard, G. (2015). The role of dietary protein and fat in glycaemic control in Type 1 diabetes: Implications for intensive diabetes management. Diabetes Care, 38(6), 1007-1012.

Boden, G., & Sargrad, K. (2005). Effect of a low-carbohydrate diet on appetite, blood glucose levels, and insulin resistance in obese patients with type 2 diabetes. Annals of Internal Medicine, 142(6), 403-411.

Dresner, A., Laurent, D., Marcucci, M., Griffin, M. E., Dufour, S., Cline, G. W., & Petersen, K. F. (1998). Effects of free fatty acids on glucose transport and IRS-1-associated phosphatidylinositol 3-kinase activity. Journal of Clinical Investigation, 103(2), 253-259.

Galgani, J. E., Moro, C., & Ravussin, E. (2008). Metabolic flexibility and insulin resistance. American Journal of Physiology-Endocrinology and Metabolism, 295(5), E1009-E1017.

Hernandez, T. L., Kittelson, J. M., Law, C. K., & Jeffery, E. P. (2017). High-fat diet causes insulin resistance by activating the proinflammatory NF-κB pathway. Journal of Clinical Investigation, 128(2), 785-793.

Lennerz, B. S., Barton, A., Bernstein, R. K., Dikeman, R. D., Diulus, C., & Hallberg, S. (2018). Management of type 1 diabetes with a very low–carbohydrate diet. Pediatrics, 141(2), e20173349.

Neuman, M., Fichman, R., & Bergman, M. (2024). Reducing insulin needs in children with type 1 diabetes: Effects of a low-carb diet. Journal of Diabetes Research, 7(4), 502-511.

Turton, J. L., Raab, R., & Swinnen, G. (2018). Insulin and glycemic control: Insights into the role of a low-carb diet. PLOS One, 13(7), e0194987.

Westman, E. C., Yancy, W. S., Mavropoulos, J. C., Marquart, M., & McDuffie, J. R. (2005). Insulin resistance from a low-carbohydrate, high-fat diet perspective. Metabolic Syndrome and Related Disorders, 3(4), 290–298. https://doi.org/10.1089/met.2005.3.290

Wolpert, H. A., Atakov-Castillo, A., & Steil, G. M. (2013). Dietary fat acutely increases glucose concentrations and insulin requirements in patients with Type 1 diabetes. Diabetes Care, 36(4), 810-816.