Acute and prolonged effects of aerobic endurance training on N‐lactoyl‐phenylalanine and inflammatory markers in individuals with type 1 diabetes: An exploratory analysis of the ULTRAFLEXI‐1 study

1. INTRODUCTION

Exercise is a cornerstone of non‐pharmacological therapy in type 1 diabetes (T1D) improving glycaemic control, cardiovascular health and overall quality of life. ¹ Acute exercise enhances glucose uptake via insulin‐independent mechanisms, while regular exercise increases insulin sensitivity, reduces glycaemic variability, improves lipid profiles, and lowers blood pressure. Collectively, these adaptations were associated with reduced risk for both, micro‐ and macrovascular complications. ¹ , ² Despite these established benefits, adherence to recommended activity levels remains low among people with T1D, often due to the fear of hypoglycemia. ³

The molecular mediators underpinning exercise‐induced benefits remain incompletely understood. Exercise‐induced signalling molecules, often termed exerkines, have emerged as potential mediators of these adaptations. For example, interleukin‐6 (IL‐6), which is released from contracting skeletal muscle, exerts dual roles in metabolic regulation and immune modulation. ⁴ While acute IL‐6 elevations during exercise are well documented, long‐term adaptations remain inconsistent across studies. ⁵ , ⁶

N‐lactoyl‐phenylalanine (Lac‐Phe), an exercise‐inducible metabolite derived from lactate and phenylalanine has recently gained attention. It is robustly induced by exercise in humans and animals, with potential roles in appetite suppression and weight regulation. ² , ⁷ To date, Lac‐Phe has not been investigated in people with T1D, a population marked by chronic low‐grade inflammation and elevated cardiovascular risk. ¹ , ² , ⁶ , ⁷ , ⁸

The present work aimed to assess acute and prolonged effects of regular moderate‐intensity exercise on selected inflammatory markers and the appetite‐regulating metabolite Lac‐Phe in adults with T1D.

2. MATERIALS AND METHODS

We analysed study samples of the ULTRAFLEXI‐1 trial, ³ a single‐centre, randomised, cross‐over study conducted at the Cardiometabolic Trials Unit at the Medical University of Graz, Austria.

Twenty‐five adults (14 males) with T1D (mean age 41.4 ± 11.9 years, body mass index 23.7 ± 3.1 kg/m², HbA1c 59 ± 9 mmol/mol) were included. All participants had T1D for ≥1 year and were treated with multiple daily insulin injections.

The underlying trial compared the effects of basal insulin glargine and degludec at two different dosages (75% and 100%) during physical exercise. For the current analysis, only exercise‐related data were evaluated. As both insulins are expected to be biologically similar, we evaluated the impact of exercise on inflammatory markers irrespective of the type of insulin treatment phases. The study was approved by the local ethics committee (31‐551 ex 18/19) and registered at the German Clinical Trials Register (DRKS00018065; drks.de).

2.1. Exercise testing protocol

Participants completed four trial phases, each consisting of 2 weeks of exercise with three cycling sessions per week. The scheduling of the exercise sessions was randomised (any 3 days from Monday to Friday). Each training session included 3 min rest, 3 min warm‐up at 20 W, 54 min cycling at 66% VO_2max, reflecting moderate exercise intensity, followed by a 3‐min cool‐down and rest. Any additional strenuous exercise was prohibited during the trial period.

2.2. Blood sampling

Blood samples were collected weekly, pre‐exercise at minute 0 (M0), during exercise at minute 30 (M30) and post‐exercise at minute 60 (M60) for Lac‐Phe, hsCRP, ferritin and IL‐6. The limit of quantification for Lac‐Phe in the local lab is 1.5 nmol/L. The intra‐day and inter‐day coefficients of variation were 3.3%–3.7% and 4.2%–5.4%, respectively. All samples were collected in a non‐fasting state and analysed at the Clinical Institute of Medical and Chemical Laboratory Diagnostics, University Hospital Graz.

2.3. Statistical methods

A linear mixed‐effects model (LMEM) with multiplicity adjustment (Holm's method) was applied to assess within‐exercise session changes (M0, M30, M60), longitudinal trends over the 8‐week training period, and interactions between acute and chronic exercise effects. In LMEM, exercise sessions were nested within study participants (random effects), while exercise sessions, timepoints within each exercise session, and insulin type were included as fixed effects. The results were reported as marginal mean ± standard error of mean (SEM).

3. RESULTS

All biomarkers analysed showed significant increases within the exercise bouts from M0 to M60 (Figure 1A–D; p2 < 0.001 for all). All biomarker levels tended numerically to decline over the 8‐week intervention, albeit only ferritin (p1 < 0.001) reached statistical significance. Biomarker pattern, analysed as an interaction between within exercise bouts and the sequence of exercise sessions, demonstrated a trend towards an interaction for Lac‐Phe (p3 = 0.0644), while no significant interaction effects were observed for the other biomarkers investigated.

FIGURE 1.

Panels (A) (Lac‐Phe), (B) (IL‐6), (C) (hsCRP), and (D) (ferritin) show the marginal mean ± SEM of biomarker trends over the 8‐week training period. P₁ = Holm‐adjusted p value for change across exercise sessions. P₂ = Holm‐adjusted p value for difference in exercise bout (M0, M30, M60). P₃ = Holm‐adjusted p value for difference between exercise bout over exercise sessions. Time points: M0 (pre‐exercise), M30 (during exercise), and M60 (post‐exercise).

4. DISCUSSION

In our analysis, all biomarkers showed significant, increasing acute levels within each exercise session underscoring the immediate physiological impact of moderate exercise, which is partly shown in prior studies. ² , ⁴ , ⁶ , ⁸

To our knowledge, this is the first analysis of Lac‐Phe under chronic exercise conditions in T1D. Initial studies focused on the effects of Lac‐Phe primarily as an exercise‐inducible metabolite with potential anti‐obesity actions, as a candidate marker for assessing individual metabolic responses to exercise, but also on its anti‐inflammatory effects. ² , ⁷ , ⁸ , ⁹ Prior studies in young healthy and physically active adults demonstrated that Lac‐Phe increases in response to acute treadmill running, sprint, and resistance exercise, with magnitude depending on exercise intensity with persisting elevations post‐exercise. ² , ⁸

Our findings extend these results, with a trend towards an interaction between exercise pattern and training session sequence demonstrating that Lac‐Phe's acute response is not static but appears to adapt over repeated sessions. This adaptive regulation supports the concept of Lac‐Phe as a metabolic signal linked to training status, potentially contributing to long‐term benefits such as appetite regulation or anti‐inflammatory effects.

Our findings showed a significant decline in ferritin levels over the 8 weeks of exercise (Figure 1), suggesting a long‐term anti‐inflammatory effect of repeated exercise, as it has been shown previously. ¹⁰

IL‐6, released by skeletal muscle during exercise, is both a pro‐ and anti‐inflammatory cytokine, with levels varying by exercise intensity and modality. ¹¹ While chronically elevated IL‐6 levels are associated with insulin resistance and muscle atrophy, transient increases post‐exercise improve skeletal muscle insulin sensitivity and induce anti‐inflammatory responses. ¹² However, our analyses showed a more variable pattern of IL‐6 levels, with both a significant time effect and a declining trend of IL‐6 response to exercise over time, as did the acute inflammatory response within the exercise session, albeit not reaching statistical significance.

Several limitations must be acknowledged; first, the study lacked a control group without regular exercise sessions. Second, only selected biomarkers were analysed, and a broader cytokine panel might have provided further mechanistic insight. Third, blood samples were collected in a non‐fasting state, which may have influenced Lac‐Phe kinetics.

5. CONCLUSION

While all biomarkers showed acute responses to exercise, a trend towards an interaction between within‐exercise pattern and session sequence for Lac‐Phe was observed. The present findings align with previous evidence, showing that Lac‐Phe is released in response to exercise and further demonstrate that this release persists under long‐term exercise conditions, with secretion patterns changing with repeated exercise sessions, indicative of adaptive regulation.

Altogether, these findings support the importance of regular moderate‐intensity exercise in promoting immunomodulatory effects and facilitating metabolic adaptation in adults with T1D.

CONFLICT OF INTEREST STATEMENT

The authors declare no conflicts of interest.

Glatz U, Müller A, Moser O, et al. Acute and prolonged effects of aerobic endurance training on N‐lactoyl‐phenylalanine and inflammatory markers in individuals with type 1 diabetes: An exploratory analysis of the ULTRAFLEXI‐1 study. Diabetes Obes Metab. 2026;28(1):771‐774. doi: 10.1111/dom.70236

DATA AVAILABILITY STATEMENT

The data are available upon reasonable requests for further research proposals from the study group, after a dedicated data transfer agreement is in place. Making the clinical dataset fully available online is challenging due to contractual obligations involved in the trial funding.