Black pepper

Continuing the discussion on the biological properties of black pepper, it is important to focus on the evidence from clinical studies on humans. While experimental research allows us to understand the cellular and molecular mechanisms of piperine, it is the studies conducted on patients and volunteers that provide more concrete indications regarding the potential metabolic and physiological impact of this spice in real-world practice.

A first element to understand is the specific role that piperine plays in clinical nutrition. Beyond the intrinsic properties of the molecule, one of the most studied aspects concerns its ability to increase the intestinal absorption of other bioactive compounds. This phenomenon is known as the “bio-enhancer” effect. In simple terms, piperine can act as a sort of biological amplifier: although present in relatively small quantities, it is able to increase the bioavailability of other substances that would otherwise be absorbed to a much more limited extent. For this reason, many clinical studies have investigated piperine in combination with other phytocompounds, particularly with curcumin, the main polyphenol in turmeric.

An interesting example comes from a double-blind, randomized clinical trial conducted on patients with non-alcoholic fatty liver disease, a condition that is extremely widespread today and closely linked to visceral obesity, insulin resistance, and dyslipidemia. In this study, sixty patients with moderate or severe fatty liver disease were treated for twelve weeks with a combination of curcumin (500 mg per day) and piperine (5 mg per day) or with a placebo. At the end of the intervention, the group treated with the combination showed significant improvements in several cardiometabolic parameters: reduction in waist circumference, decrease in systolic blood pressure, reduction in total cholesterol and LDL, as well as better control of fasting glycemia. In parallel, reductions in liver enzymes ALT and AST, which are indicators of liver damage, were observed (Sharifi et al., 2023) [6].

A similar picture also emerges in research conducted on patients with type 2 diabetes. In a randomized clinical trial, seventy-one diabetic patients received a daily supplementation of turmeric combined with piperine or a placebo for four months. At the end of the intervention, significant reductions were observed in fasting glycemia, glycated hemoglobin (HbA1c), the HOMA-IR index (an indicator of insulin resistance), and plasma triglycerides. In other words, the combination of the two compounds, piperine and curcumin, produced an overall improvement in metabolic control, suggesting a possible role as a nutraceutical support in the integrated management of diabetes, albeit without replacing standard pharmacological therapies (Figueiredo Neta et al., 2021) [7].

Interesting data also emerge in the context of cardiovascular diseases. In a randomized clinical trial conducted on patients with acute myocardial infarction, supplementation with curcumin combined with piperine for eight weeks led to significant improvements in some metabolic parameters, including a reduction in HbA1c and an improvement in the lipid profile with a decrease in LDL and an increase in HDL: this suggests that the main effect of the supplementation may concern metabolism and systemic inflammation (Tabaee et al., 2021) [8].

Another area in which the curcumin-piperine combination has been studied concerns inflammatory bowel diseases, such as ulcerative colitis and Crohn's disease. In a randomized clinical trial conducted on patients with mild-to-moderate forms of these pathologies, twelve weeks of supplementation with curcumin combined with piperine led to an improvement in body composition, with an increase in lean mass and an increase in the phase angle, a bioimpedance parameter associated with the quality of cellular status. These results are particularly interesting because in inflammatory bowel diseases, it is common to observe a combination of excess adipose tissue and loss of muscle mass, a condition that can worsen the clinical prognosis. The increase in lean mass therefore suggests a possible metabolic and nutritional benefit of the supplementation (Martins et al., 2025) [9].

Alongside chronic supplementation studies, there is also research that has evaluated the acute effects of black pepper directly within meals. In a crossover study conducted on healthy adults, researchers analyzed the effect of adding black pepper and turmeric to a standard breakfast containing carbohydrates. The results showed that the presence of black pepper, alone or in combination with turmeric, significantly reduced postprandial glycemia compared to the control meal. In parallel, participants reported a reduction in perceived hunger and a greater feeling of satiety in the hours following the meal. These effects suggest that some spices can modulate the metabolic response to glucose and influence appetite regulation signals, even when used simply as culinary ingredients (Khan et al., 2024) [10].

Taken together, this evidence suggests that black pepper, and in particular piperine, does not act only as an isolated bioactive compound, but also as a modulator of the efficacy of other nutrients and phytocompounds. It is as if this molecule functions as a “biological facilitator,” capable of increasing the efficiency with which certain substances are absorbed and used by the body. This role explains why piperine is frequently included in nutraceutical formulations intended to improve the bioavailability of molecules that are otherwise poorly absorbed.

Naturally, it is important to interpret these results with caution. Most of the available clinical studies have relatively limited sample sizes and moderate duration, and often analyze piperine in combination with other compounds. However, the overall picture suggests that supplementation containing piperine can influence various aspects of human metabolism, particularly those related to glycemic, lipid, and inflammatory regulation.

In other words, what for centuries has been simply an ingredient in daily cooking reveals itself, in light of modern scientific evidence, to be a small but sophisticated modulator of human metabolism.

Continuing the analysis of the potential pathophysiological applications of piperine, in recent years, researchers' attention has also focused on certain metabolic and oncological conditions—areas where the biological properties of this alkaloid appear to manifest in a particularly interesting way. Although much of the available evidence still derives from experimental studies or relatively small clinical trials, the results obtained help to outline the potential role of piperine as a nutraceutical compound capable of modulating metabolic, inflammatory, and proliferative processes.

One of the most studied areas concerns non-alcoholic fatty liver disease (NAFLD), a condition characterized by the accumulation of lipids in the liver in the absence of significant alcohol consumption and closely associated with visceral obesity, insulin resistance, and metabolic syndrome. In a double-blind, placebo-controlled randomized clinical trial, the administration of curcumin combined with piperine for eight weeks resulted in a significant reduction in the ultrasound severity of fatty liver in the treated subjects compared to the placebo group. In parallel, a reduction in alkaline phosphatase was observed, a biochemical indicator often associated with liver dysfunction and chronic inflammation. The authors hypothesized that these effects may be attributed to the combination of the antioxidant, anti-inflammatory, and metabolic activities of the two compounds, in addition to the ability of piperine to increase the bioavailability of curcumin (Mirhafez et al., 2021) [11].

Another controlled clinical trial directly analyzed the effects of piperine in patients suffering from NAFLD associated with early-stage cirrhosis. In this trial, participants received a daily supplementation of piperine (5 mg) for twelve weeks. At the end of the intervention, the treated group showed a significant reduction in the liver enzymes AST and ALT, indicators of hepatocellular damage, along with improvements in glucose metabolism and the lipid profile. A reduction in insulin resistance indices was also observed, suggesting that piperine may exert a favorable effect on the metabolic axis that connects the liver, lipid metabolism, and the regulation of glycemia (Nouri-Vaskeh et al., 2024) [12].

Alongside studies on metabolic diseases, a substantial part of the scientific literature has focused on the possible role of piperine in oncology. Numerous preclinical studies have, in fact, highlighted that this alkaloid can interfere with various cellular processes involved in the growth and survival of tumor cells. Among the most frequently described mechanisms are the induction of apoptosis, cell cycle arrest, the modulation of oncogenic signaling pathways, and the reduction of metastasis and angiogenesis processes. Piperine also appears to influence key molecular pathways such as NF-κB, STAT3, PI3K/AKT, and MAPK, which regulate cell proliferation, inflammation, and resistance to programmed cell death. This multi-target nature makes the molecule particularly interesting as a potential chemopreventive agent or as an adjuvant in anticancer therapies (Cinar and Sanlier, 2025) [13].

Some experimental studies have analyzed in greater detail the molecular mechanisms through which piperine can induce tumor cell death. In cellular models of gastric carcinoma, for example, treatment with piperine showed the ability to reduce tumor cell proliferation and increase apoptosis in a dose-dependent manner. This effect appears closely linked to the generation of reactive oxygen species and the consequent mitochondrial dysfunction. The increase in ROS, in fact, leads to a loss of mitochondrial membrane potential and alters the balance between pro- and anti-apoptotic proteins such as Bax and Bcl-2, favoring the release of cytochrome c and the activation of the caspases responsible for the apoptotic cascade. Overall, these results suggest that piperine can activate the mitochondrial apoptotic pathway in tumor cells, contributing to the reduction of neoplastic growth (Guo et al., 2021) [14].

Similar evidence has also emerged in models of chronic myeloid leukemia. In a study conducted on the K-562 cell line (human tumor cells derived from a patient with chronic myeloid leukemia), both black pepper extract and pure piperine showed significant cytotoxic and antiproliferative activity. The treatment resulted in an increase in the expression of the pro-apoptotic genes Bax, caspase-3, and caspase-9, accompanied by a reduction in the expression of the anti-apoptotic protein Bcl-2. In parallel, a decrease in cellular proliferative activity was observed, associated with the down-regulation of the PCNA protein, a marker of cell replication. Taken together, these results suggest that piperine can simultaneously interfere with the mechanisms that regulate both the survival and the proliferation of tumor cells (Banerjee et al., 2021) [15].

Considered as a whole, this evidence indicates that piperine possesses an extremely complex biological profile, capable of influencing not only metabolic processes but also cellular mechanisms involved in cell proliferation and death. However, it is fundamental to emphasize that a large part of the available oncological evidence still derives from in vitro or animal experimental models. Consequently, although the results are promising, further clinical studies on humans will be necessary to precisely define the therapeutic role of piperine and to establish dosages, safety, and possible real-world clinical applications.

One of the most interesting aspects of piperine concerns its ability to act directly on the main biological mechanisms underlying insulin resistance, a condition that represents the pathophysiological core of type 2 diabetes, non-alcoholic fatty liver disease, and metabolic syndrome. In the presence of insulin resistance, peripheral tissues become progressively less sensitive to insulin signaling, forcing the pancreas to maintain chronic compensatory insulin hypersecretion. This state of persistent hyperinsulinemia fuels systemic inflammation, oxidative stress, lipid accumulation, and continuous activation of the PI3K/AKT/mTOR pathway.

In this context, piperine appears to act as a multifactorial metabolic modulator, capable of simultaneously intervening in glucose metabolism, energy homeostasis, and insulin signaling. One of the most interesting pieces of evidence emerges from studies conducted on animal models of diet-induced obesity. In rats fed a high-fat diet, piperine administration significantly improved insulin sensitivity, reduced hepatic fat accumulation, and attenuated steatosis (Wang et al., 2022) [16]. At the same time, an improvement in the lipid profile was observed, with a reduction in triglycerides, total cholesterol, and free fatty acids.

From a pathophysiological perspective, this finding is extremely important because the abnormal accumulation of lipids in the liver represents one of the main drivers of hepatic insulin resistance. When the liver accumulates excessive amounts of fat, the response to insulin is progressively impaired, promoting hyperglycemia, increased gluconeogenesis, and further compensatory hyperinsulinemia. Piperine appears to break this vicious cycle through the activation of AMPK (Wang et al., 2022) [16], promoting lipid oxidation and improving cellular energy homeostasis.

This step is particularly relevant because AMPK represents one of the main physiological antagonists of chronic mTOR hyperactivation. When AMPK is activated, the cell progressively reduces lipogenesis, energy storage, and continuous anabolic stimulation, favoring a condition of greater metabolic flexibility.

The relationship between piperine and insulin signaling emerges with even greater clarity in studies focused directly on the IR/AKT/GLUT4 pathway. In animal models of diabetes induced by a high-fat and sucrose diet, piperine significantly improved fasting glycemia, HbA1c, and insulin homeostasis (Prasad et al., 2023) [17]. At the molecular level, the treatment increased the expression of IRS-1, AKT, and GLUT4 at both the protein and transcriptional levels.

This finding is biologically very important because GLUT4 represents one of the main transporters responsible for the entry of glucose into muscle and adipose tissue in response to insulin. In conditions of insulin resistance, the translocation of GLUT4 to the cell membrane is compromised, reducing peripheral glucose uptake. Piperine, on the other hand, seems to "reopen" this metabolic pathway, improving the cellular capacity to utilize glucose without requiring continuous insulin hypersecretion.

Computational simulations have also shown a high affinity of piperine for key insulin signaling proteins, including IR, IRS-1, AKT, GLUT4, and AS160 (a key protein in human metabolism that regulates glucose) (Prasad et al., 2023) [17]. Conceptually, this suggests that piperine does not act only indirectly by reducing inflammation or oxidative stress, but may interact directly with the main intracellular regulators of glucose metabolism.

A further particularly interesting element concerns the relationship between piperine, inflammation, and insulin sensitivity. In a mouse model characterized by chronic fructose and glucose intake, piperine significantly reduced glycemia and the HOMA-IR index, while simultaneously improving GLUT-4 expression and AKT phosphorylation (Oladayo et al., 2026) [18]. Concurrently, a marked reduction in the activation of NF-κB, one of the main mediators of chronic inflammation associated with insulin resistance, was observed.

This aspect is extremely relevant because the persistent activation of NF-κB promotes the production of pro-inflammatory cytokines that directly interfere with insulin signaling. It is as if chronic inflammation is continuously "disturbing" the dialogue between insulin and the cellular receptor. By reducing NF-κB and improving the AKT/GLUT4 pathway, piperine appears to help restore more efficient metabolic communication (Oladayo et al., 2026) [18].

The relationship between piperine and insulin resistance is also confirmed by clinical studies in humans. In a randomized, placebo-controlled, double-blind study conducted on patients with non-alcoholic fatty liver disease and early cirrhosis, the intake of 5 mg/day of piperine for 12 weeks resulted in a significant reduction in glycemia and insulin resistance, with an improvement in the HOMA-IR index compared to the placebo group (Nouri-Vaskeh et al., 2024) [12].

At the same time, the treated patients showed improvements in liver enzymes and the lipid profile. This finding is particularly important because it confirms in humans what has already been observed in experimental models: piperine appears to act simultaneously on glucose metabolism, lipid metabolism, liver function, and systemic inflammation; the authors also emphasize that these effects could depend on the activation of the AMPK and PI3K/AKT pathways, the reduction of pro-inflammatory cytokines, and the improvement of mitochondrial function (Nouri-Vaskeh et al., 2024) [12]. Once again, a coherent picture emerges in which energy metabolism, inflammation, and insulin signaling are deeply interconnected.

Overall, the available evidence shows that black pepper does not act simply as an aromatic spice or bioavailability enhancer, but as a true modulator of metabolic physiology. Through piperine, this spice appears to improve insulin sensitivity, increase peripheral glucose uptake, reduce chronic inflammation, and promote more efficient cellular energy rebalancing.

In this sense, the relationship between black pepper and insulin resistance represents one of the most interesting examples of how a natural compound can interact with the main biological nodes of modern metabolic diseases, helping to counteract the effects of chronic hyperinsulinemia and continuous hyperactivation of the insulin pathway.

A particularly interesting aspect that has emerged in recent years concerns the relationship between piperine and one of the main regulators of cellular metabolism and growth: the PI3K/AKT/mTOR pathway. This signaling cascade represents one of the central nodes of cellular physiology, as it controls fundamental processes such as proliferation, cell survival, protein synthesis, and autophagy. It is therefore not surprising that its hyperactivation has been associated with numerous chronic diseases, including cancers, neurodegenerative diseases, and metabolic disorders. In this context, several experimental studies have highlighted how piperine can modulate this signaling pathway, profoundly influencing the fate of cells.

In cellular models of colorectal carcinoma, for example, it has been observed that piperine is able to significantly reduce the viability of tumor cells and induce cell cycle arrest in the G1 phase (the phase in which the cell grows, produces proteins, and prepares to duplicate its DNA). This effect is accompanied by a decrease in the expression of cyclin E and an increase in the cell cycle inhibitor p27, two key proteins that regulate the transition between the growth phase and DNA replication. In parallel, treatment with piperine increases the intracellular production of reactive oxygen species and suppresses the activity of the PI3K/AKT pathway, one of the main survival pathways for tumor cells. Together, these changes create an intracellular environment hostile to proliferation, instead favoring the activation of programmed cell death pathways (Chang et al., 2025) [19].

The modulation of this signaling pathway also appears to play a central role in the induction of autophagy, a process through which the cell degrades and recycles damaged or non-functional components. Under physiological conditions, autophagy represents a cellular maintenance mechanism; however, when it is intensely activated in tumor cells, it can contribute to their death. Studies conducted on human oral carcinoma cells have shown that piperine reduces cell viability by simultaneously inducing apoptosis and autophagy, two cell death programs that in this case appear to mutually enhance each other. At the root of this effect is a suppression of the PI3K/AKT/mTOR pathway, which normally acts as a brake on autophagy. When this brake is removed, the autophagic process can be activated more intensely, contributing to the reduction of tumor growth (Han et al., 2023) [20].

A similar mechanism has also been observed in colorectal carcinoma, where piperine appears to act through a dual modulation: on one hand, it increases the production of reactive oxygen species, and on the other, it reduces the activity of the AKT/mTOR pathway. This combination of oxidative stress and inhibition of survival signals creates a cellular context favorable to the activation of autophagy and the consequent reduction of tumor cell viability. When researchers artificially reactivated the AKT pathway or neutralized ROS with antioxidants, the antitumor effects of piperine were significantly attenuated, suggesting that these two elements represent key steps in the mechanism of action (Xia et al., 2024) [21].

The influence of piperine on the PI3K/AKT/mTOR pathway does not seem to be limited to the oncological field. In animal models of ischemic stroke, the administration of this alkaloid has shown significant neuroprotective effects. In rats subjected to middle cerebral artery occlusion, treatment with piperine reduced the area of cerebral infarction, improved neurological performance, and preserved the structural integrity of neurons. At the molecular level, these effects were associated with a modulation of the PI3K/AKT/mTOR pathway and a regulation of the autophagic processes that are activated during ischemic damage. In other words, piperine appears to contribute to restoring a balance in the cellular mechanisms that determine the survival or death of nerve cells after an ischemic event (Zhang et al., 2022) [22].

An equally interesting perspective emerges from studies on Parkinson's disease, a neurodegenerative pathology characterized by the abnormal accumulation of the protein α-synuclein and the progressive loss of dopaminergic neurons. In experimental animal models, it has been observed that piperine can reduce the accumulation of this protein both in the brain and in the colon, suggesting an involvement of the gut-brain axis in the pathogenesis of the disease. In this case, too, the mechanism appears to involve the modulation of the PI3K/AKT/mTOR pathway and the activation of autophagy, which promotes the degradation of aggregated proteins. In parallel, animals treated with piperine show improvements in both motor parameters and intestinal function, indicating that the compound could act on multiple levels of the pathological process (Yu et al., 2024) [23].

Taken together, these findings suggest that piperine possesses the ability to interact with one of the main control centers of cellular metabolism represented by the PI3K/AKT/mTOR pathway. Rather than acting on a single molecular target, this alkaloid appears to modulate a complex network of intracellular signals that regulate proliferation, oxidative stress, autophagy, and cell death. It is as if the molecule were able to intervene in a sort of "metabolic control unit" of the cell, influencing the balance between growth and cellular self-destruction. This very multi-target nature represents one of the most fascinating aspects of bioactive compounds of plant origin and explains why black pepper, a spice used daily in cooking, continues to arouse strong interest in biomedical research today.

If the relationship between piperine and the PI3K/AKT/mTOR pathway already shows significant biological relevance, the picture becomes even more interesting when observing the role of AMPK, the primary cellular energy sensor. As discussed in previous chapters, AMPK and mTOR represent two opposing but complementary metabolic programs: when nutrients, glucose, and insulin are abundant, mTOR promotes cell growth, protein synthesis, and energy storage; conversely, when the cell senses energy stress or reduced ATP availability, AMPK slows down anabolic processes, reactivates autophagy, and promotes the restoration of metabolic homeostasis. In this delicate balance, piperine appears to act as a modulator capable of restoring the proper dialogue between these two systems.

One of the most interesting aspects emerges from studies on luminal A breast cancer. Through integrated approaches of molecular docking, dynamic simulations, and in vitro biological validation, it has been demonstrated that piperine binds directly to AMPK with an affinity comparable to that of metformin (Jan et al., 2026) [24]. Molecular simulations showed a conformational stabilization of the piperine–AMPK complex, suggesting a persistent functional interaction with the enzyme's regulatory site. From a conceptual standpoint, this finding is extremely relevant because it indicates that piperine does not act only "downstream" by modulating secondary metabolic signals, but can interact directly with one of the main cellular energy sensors.

At the biological level, this interaction translates into a significant reduction in cell viability and the induction of apoptosis (Jan et al., 2026) [24]. The activation of AMPK appears closely linked to the inhibition of mTOR-dependent proliferative signals, suggesting that piperine progressively pushes the tumor cell out of a continuous and metabolically dysfunctional growth mode. It is as if the molecule forces the cell to "recognize" its actual energy state, interrupting artificial proliferation programs sustained by anabolic hyperactivation.

This energy regulation also appears particularly evident in the nervous system. In experimental models of ischemic stroke, piperine significantly improved neuronal mitochondrial function, reduced the production of reactive oxygen species, and increased intracellular ATP availability through the activation of AMPK (Xi et al., 2026) [25]. In parallel, an increase in the expression of Apelin-13, a peptide involved in neuronal protection and cellular energy regulation, was observed.

This aspect is extremely important because it links AMPK activation not only to glucose metabolism but also to mitochondrial biogenesis and cellular resilience. During cerebral ischemia, in fact, the loss of mitochondrial function leads to energy collapse, ROS accumulation, and neuronal death. Piperine, on the other hand, seems to favor the recovery of cellular energy balance by stimulating the production of new functional mitochondria through AMPK (Xi et al., 2026) [25].

From a physiological perspective, this means that piperine does not act simply as an antioxidant, but as a regulator of the entire cellular energy response. It is as if it helps the cell to "reignite" its energy production system under conditions of severe metabolic stress.

The ability of piperine to activate AMPK also emerges with great clarity in skeletal muscle, one of the main organs involved in energy homeostasis and insulin sensitivity. In mouse muscle cells, piperine significantly increased the intracellular AMP/ATP ratio, stimulating the phosphorylation of AMPK (Kim et al., 2017) [26]. Concurrently, an increase in the translocation of GLUT4 to the plasma membrane was observed, resulting in increased glucose uptake.

Particularly interesting is the role of intracellular lactate. Traditionally considered only a byproduct of anaerobic glycolysis, in this study, lactate emerges as a true signaling molecule capable of activating metabolic programs associated with thermogenesis and mitochondrial function. Piperine has, in fact, increased the expression of a mitochondrial protein involved in energy expenditure and insulin sensitivity through an AMPK-dependent mechanism.

This finding is particularly relevant because it shows how piperine can contribute to improving cellular metabolic flexibility. When AMPK is activated, the cell progressively reduces its permanent anabolic state, indirectly limiting the chronic hyperactivation of mTOR typical of persistent hyperinsulinemia.

An analogous mechanism also emerges in studies on muscle glucose metabolism in mice: piperine increased glucose uptake through the pathway involving AMPK, promoting GLUT4 translocation and improving glycemic homeostasis (Maeda et al., 2018) [27]. AMPK activation was dependent on the increase in intracellular calcium and moderate ROS production.

This aspect is biologically very interesting because it shows how low, controlled levels of ROS can act as physiological metabolic signals rather than exclusively as harmful elements. Through this "fine" activation of the AMPK pathway, piperine seems to improve peripheral glucose utilization without further overloading the insulin pathway already hyperstimulated in conditions of insulin resistance; the study also demonstrated that pharmacological inhibition of AMPK completely abolished the effects of piperine on GLUT4 translocation, confirming the central role of this kinase in the molecule's mechanism of action (Maeda et al., 2018) [27].

Overall, the available evidence outlines piperine as an extremely sophisticated energy modulator. Through the activation of AMPK and the indirect reduction of pathological mTOR hyperactivation, black pepper seems to promote autophagy, mitochondrial biogenesis, energy oxidation, glucose transport, and cellular adaptation to metabolic stress.

In a context characterized by chronic hyperinsulinemia, caloric overload, and continuous anabolic stimulation, the relationship between black pepper, AMPK, and mTOR therefore takes on a meaning deeply consistent with what was discussed in the previous chapters: helping the cell exit a forced and metabolically dysfunctional growth mode, returning it toward a condition of greater energy balance, resilience, and metabolic flexibility.