Why Normal Weight People With Type 2 Diabetes Should Emphasize Strength Training

The prevalence of type 2 diabetes is increasing and it has been associated with a high burden of morbidity and mortality⁽¹⁾. It’s characterized by insulin resistance, where the body’s cells don’t respond well to insulin, a hormone that regulates the movement of sugar into cells. As a result, the pancreas produces more insulin to try to get cells to respond. Over time, the pancreas can't keep up, and blood sugar levels rise.

Although most people with type 2 diabetes are overweight/obese, approximately 20% are in the healthy weight body mass index (BMI) category (<25 kg/m2), herein defined as ‘normal-weight type 2 diabetes’, which is recognized as a different phenotype that is more common in Asian populations and older adults⁽²⁾. 

When compared with overweight/obese subgroups, individuals with a normal weight at diagnosis of type 2 diabetes are shown to have a higher risk of mortality than those who are overweight or obese⁽²⁾.

Research indicates that this subgroup of people with normal-weight type 2 diabetes are associated with sarcopenia, or loss of muscle mass⁽³⁾.

The loss of skeletal muscle creates a huge burden to health. It’s clear from scientific research, that losing skeletal muscle is the catalyst in many types of diseases from metabolic syndrome to Alzheimer’s disease.

In addition, studies suggest that this reduced muscle size mediates the elevated mortality risk in people with normal-weight diabetes compared with overweight people with type 2 diabetes⁽²⁾.

In general, exercise is suggested for individuals with type 2 diabetes.

Clinical guidelines recommend similar exercise for individuals with type 2 diabetes as is recommended for the general population: 3–5 days per week of aerobic activity at moderate to vigorous intensity, achieving a minimal exercise duration of 150 min per week, and two to three sessions per week of strength training⁽⁴⁾.  

The effects of specific types of exercise (strength vs aerobic) on hemoglobin A1C (HbA1c) levels have been investigated previously, but these trials have predominantly been carried out in people who are overweight/obesity with type 2 diabetes. 

An HbA1c test is a blood test that shows what your average blood sugar (glucose) level was over the past two to three months.

These previous studies indicate that in the overweight/obese population; a combination of aerobic and strength training seem to be superior than either aerobic or strength training alone⁽⁵⁾.

Individuals with obesity have both increased fat and increased lean muscle mass⁽⁶⁾, while individuals who are normal-weight with type 2 diabetes are more prone to have sarcopenia (loss of muscle mass), especially related to fat mass (relative sarcopenia).

In reference to the relative sarcopenia in people with normal-weight type 2 diabetes compared with those with type 2 diabetes and obesity, the most effective exercise regimen for individuals with overweight/obesity with type 2 diabetes may not be ideal for the normal-weight population.

A very recent study called the “Strength Training Regimen for Normal Weight Diabetes (STRONG-D)” study compared the effects of strength training alone, aerobic training alone and a combination of strength and aerobic training on glycemic control in individuals with normal-weight (BMI <25 kg/m2) type 2 diabetes.

Major outcome measures were changes in body composition and muscle strength resulting from these exercise interventions and assessed the impact of body composition changes on HbA1c⁽⁷⁾.

This research was well controlled and followed very sound guidelines.  The researchers conducted a randomized controlled trial with participants aged 18-80 years, having a BMI <25 kg/m² and type 2 diabetes.

They were divided into three groups:
1. Strength training (ST)
2. Aerobic training (AER)
3. a combination of strength & aerobic training (COMB)

Each group followed a 9-month exercise program, and the primary outcome was the change in HbA1c levels at 3, 6, and 9 months, with secondary outcomes including changes in body composition at 9 months. Per adherence to recommended exercise protocol, analysis included participants who completed at least 50% of the sessions.

Major findings of this study

The primary finding from this research is that strength training alone was more effective than aerobic training alone at reducing HbA1c levels in normal-weight individuals with type 2 diabetes, and combination training had an intermediate effect.

Figure: Results clearly show the decrease in the ST (strength training) group compared to the AER (aerobic) and COMB (strength & aerobic) group in HbA1c(7)

Furthermore, strength training increased appendicular lean mass relative to fat mass which was an independent predictor of the reduction in HbA1c level. This was the first clinical trial of exercise in normal-weight individuals with type 2 diabetes, who make up 20% of the population with type 2 diabetes⁽²⁾.

Although these findings need to be confirmed by additional studies, these results could be applied immediately to exercise recommendations for people with type 2 diabetes and a BMI <25 kg/m2.

The major difference in this study compared to other previous research investigating the effects of exercise on type 2 diabetes and glycemic control is that this study was designed to examine normal-weight individuals with type 2 diabetes.

This study found that strength training led to a larger reduction in HbA1c levels than aerobic training alone.

In addition, only the strength training group showed a significant reduction in HbA1c levels, suggesting a potentially unique benefit of strength training in normal-weight individuals with type 2 diabetes.  

Compared with the participants with overweight/obesity in previous research, the normal-weight participants in this current study had a lower fat mass (21.8 kg vs 37.1 kg) and lean mass (42.8 kg vs 57.7 kg). Given that 80% of insulin-mediated glucose uptake occurs in skeletal muscle (lean mass)⁽⁸⁾, one should consider the importance of increasing lean mass for improving glycemic control in this population.

An important finding of this research is that body composition change (increase in lean mass with loss of fat mass) was independently associated with a reduction in HbA1c levels. Strength training led to increased muscle mass relative to decreased fat mass in our study, and this seems to be more beneficial for lowering HbA1c levels in individuals with normal-weight type 2 diabetes, which is associated with relative sarcopenia⁽³⁾.

In contrast, overweight/obese individuals in previous studies had excess fat mass with adequate lean mass; thus, loss of fat mass in individuals with a higher BMI may be more essential for lowering HbA1c levels.  

These current findings, along with previous studies that have demonstrated a relationship between body composition and cardiovascular disease mortality indicated the importance of strength training in the normal-weight diabetes population.

Summary

This research indicates that for individuals with normal-weight type 2 diabetes, strength training is more effective than aerobic training alone in reducing HbA1c levels in normal-weight individuals with type 2 diabetes. Combining both types of training did not provide a significant advantage in terms of blood glucose control.

Additionally, the study emphasizes the importance of considering changes in body composition as a factor in the effectiveness of exercise interventions for managing type 2 diabetes. The increase in appendicular lean mass relative to fat mass was an independent predictor of reduced HbA1c levels.

As far as the impact clinically, these findings could be applied immediately to exercise recommendations for people with type 2 diabetes and a BMI <25 kg/m2.

In addition to weight training, there are supplements that are known to help regulate blood sugar. You can learn more about them here.


References:
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    5.    Church TS, Blair SN, Cocreham S, et al: Effects of aerobic and resistance training on hemoglobin A1c levels in patients with type 2 diabetes: a randomized controlled trial. JAMA 304:2253-62, 2010
    6.    Forbes GB, Welle SL: Lean body mass in obesity. Int J Obes 7:99-107, 1983
    7.    Kobayashi Y, Long J, Dan S, et al: Strength training is more effective than aerobic exercise for improving glycaemic control and body composition in people with normal-weight type 2 diabetes: a randomised controlled trial. Diabetologia 66:1897-1907, 2023
    8.    DeFronzo RA, Tripathy D: Skeletal muscle insulin resistance is the primary defect in type 2 diabetes. Diabetes Care 32 Suppl 2:S157-63, 2009