The study shows that protein-restricted dietary nutrition results in superlative phenotypes than high-fat diets. The study also shows that stress experienced during early developmental stages in life (larvae) could lead to reduced activity due to reduced impulse transduction (16). However, this favors the development of adaptive changes with increased foraging for food, resulting in an increased body mass, demonstrating evolutionary changes that would favor survival during adulthood (11). Furthermore, the study findings are similar to those of previous studies where diet restriction improved the ability to resist stress (13), increased mitochondrial density and respiratory activity, enhanced fat metabolism and physical activity (22). Besides, high fat diet-induced obesity showed a ≥ 50% reduction in Drosophila’s competitive ability (10,23). On the other hand, overnutrition during childhood would lead to the development of laziness and reluctance to forage for food, and this would justify the decreased activity in adults exposed to a lot of food in childhood. DR-induced obesity modelling in Drosophila did not affect the nervous coordination potential of obese flies. Thus, it caused higher competitive ability, unlike HFD- and HSD-induced obesity models that negatively affected nervous coordination ability, causing lesser competitive ability. These results are supported by previous studies, which reported competitive ability under obese conditions is independent of the level and degree of adiposity (24). Findings in this study demonstrate the reliability of Drosophila as a research model to study metabolic and evolutionary conditions in humans (9,10).
We also showed that DR in adulthood caused increased triglycerides, sterols and high catalase activity. These findings demonstrate the improved metabolic state in the Drosophila phenotype. Triglycerides provide energy, and these are markers of obesity in Drosophila (8). Increased energy storage versus expenditure is associated with improved antioxidant balance, which is important to control reactive oxygen species arising from oxidation of lipids and oxidative stress (25,26). The major storage forms of sterols in Drosophila is dehydrocholesterol and ergosterol (19). The DR phenotype had the highest levels of sterols than the HFD and HSD fed obese flies, and mechanisms for these differences remain to be explored.
Total protein levels were highest in HSD, providing evidence that HSD-induced obesity in Drosophila could face major increased protein levels compared to HFD. This is because HFD has been associated with increased lipid peroxidation, which causes increased tissue death and reduced lifespan in Drosophila (27,28). Furthermore, HSDs are characterized by a hypertonicity-a condition that hastens autolysis (29). On the other hand, challenges observed with HFD and HSD models help identify them as better cancer research models (30). High catalase activity demonstrates the superlative advantage associated with DR for the induction of obesity in Drosophila. Increased endogenous catalase enzyme activity serves as a natural defense mechanism against oxidative stress in pathological conditions such as obesity (31). Our findings are similar to previous studies that reported DR association with increased mitochondrial density and respiratory activity, causing elevated antioxidant enzyme activity. This is unlike the HFD and HSD fed obese flies which were associated with high levels of oxidative stress and tissue death (15,22). Furthermore, sugar diets at either low or high supplementation alter physiological function (reproduction) due to body size changes and organ size (32).
In this study, induction of obesity by DR produced a competitively more active and obese fly phenotype compared to the HFD and HSD fed obese phenotypes. The study's findings demonstrate a need to explore more active and appropriate models for modeling obesity, emphasizing evolutionary adaptive changes to promote knowledge on healthy metabolic obesity.
Molecular markers describing the metabolism of triglycerides were not investigated in this study due to financial and infrastructural challenges. Further studies would emphasize the crosstalk between a balanced diet and obesity to generate knowledge to address metabolic obesity. This would enhance further understanding of the immunological modulators of inflammation, second messengers and modulators of gene expression that can lead to the development of novel therapeutical options and healthy lifestyles.