Miku ja muut ravintotieteilijät huulipyöreänä sen tosiasian edessä, että lihakset käyttävät ja säilövät energiarasvan tyydyttyneinä rasvoina.
Terveellä kestävyysurheilijalla löytyy lihaksen sisäisiä rasvavarastoja, jotka pitää sisällään nimenomaan tyydyttyneitä rasvahappoja.
Sairaalla T2D potilaalla on lihaksiin puskettu ylimäärä rasvaa, joka on pääasiassa ”pehmeää” rasvaa. Ja muutenkin kyky käyttää rasvaa energiaksi on surkea.
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Our findings show that maladaptive intramyocellular skeletal muscle changes seen in the early stages of type 2 diabetes can be successfully reversed to a great extent. These data support the concept that skeletal muscle insulin resistance could be the primary defect in type 2 diabetes, as some have proposed
15,
16. Although further work would be required to elucidate the causality between muscle insulin resistance and intramyocellular lipid accumulation, these findings suggest that saturation of the ectopic intramyocellular lipid accumulation could be a new target for health improvement in type 2 diabetes.
The concept that saturated fat can be beneficial, especially when stored, challenges the traditional view that associates all saturated fat with an increased risk of cardiovascular disease and worse clinical outcomes.
Structured physical exercise is a cheap but effective lifestyle intervention with powerful prognostic outcomes proven in general populations, and patients with cardiac conditions or diabetes
17,
18. Due to known sex differences in intramyocellular lipid stores and utilisation rates (both higher in women
19) in this initial exploration we studied only male participants to maintain a reasonable sample size for such an intensive study protocol. To age-match the groups we recruited recreational competitive athletes according to the European Society of Cardiology definition
20, involved in endurance training, as elite athletes do not exist in this age group.
Our clinical trial reveals that, contrary to its known bad press, saturated fat is in fact essential for high level performance of skeletal muscle and its reduced intramyocellular availability or utilisation is tracking with the insulin resistant status and metabolic dysfunction of people with type 2 diabetes. The skeletal muscle lipidomic analysis detected no baseline or exercise-induced differences in total levels of saturated versus unsaturated tri/di-acylglycerols or ceramides between athletes and patients with type 2 diabetes. This apparent difference between the spectroscopic and lipidomic evaluations is rooted in two important technical aspects: firstly, spectroscopy assesses proportions of saturated/unsaturated carbon bonds present only in intramyocellular lipid stores, whereas lipidomics reports whole fatty acids per se, which are present in the intra- as well as extramyocellular compartments, including the cell membranes. Saturated fatty acids generally represent a much smaller component of the skeletal muscle lipid composition compared to the unsaturated ones, as for any given carbon length there is only one saturated fatty acid and numerous unsaturated ones. However, our MRI assessment of saturated/unsaturated carbon bonds shows that the saturated fraction of the intramyocellular lipid storage is much higher in athletes compared to patients with type 2 diabetes.
Given the dogma that saturated fat is harmful mainly through its contribution to atherosclerosis-related pathology, it is rather surprising that intramyocellular lipid saturation is reduced in patients with type 2 diabetes. Although the total intramyocellular pool did not reduce in size after patients’ endurance training, its composition did alter, with increased saturation after exercise training, at least for the duration of exercise taken during our study.
One possible explanation for these findings is that compared to saturated fatty acid metabolism, β-oxidation of unsaturated fatty acids requires two additional energy-consuming catalytic reactions, one by an isomerase and one by a reductase enzyme21,22. Therefore, overall, β-oxidation of an unsaturated fatty acid with the same chain length as a saturated fatty acid will yield less energy23.
Whilst it is understandable that with training, the skeletal muscle of healthy athletes will tend to store its fuel in a more efficient way (i.e. saturated fat), as it yields more energy, it is less clear why insulin resistant status would be associated with unsaturated intramyocellular storage. This finding cannot be attributed to differences in diets or changes in nutritional intake since participants were instructed to avoid dietary changes. Even though the 1-week food diaries almost certainly under-reported their true intake, which is a well documented phenomenon
24, importantly, there was no significant change between or within groups (except the athletes’ sugar drinks requirements which were discontinued during deconditioning). Therefore, we conclude that skeletal muscle lipid saturation could represent a new biomarker of metabolic health in type 2 diabetes.