Abstract
A high-fat diet (HFD) induces changes in gut microbiota leading to activation of pro-inflammatory pathways, and obesity, as a consequence of overnutrition, exacerbates inflammation, a known risk factor not only for cancer. However, experimental data showed that the composition of dietary fat has a greater impact on the pathogenesis of cancer than the total fat content in isocaloric diets. Similarly, human studies did not prove that a decrease in total fat intake is an effective strategy to combat cancer. Saturated fat has long been considered as harmful, but the current consensus is that moderate intake of saturated fatty acids (SFAs), including palmitic acid (PA), does not pose a health risk within a balanced diet. In regard to monounsaturated fat, plant sources are recommended. The consumption of plant monounsaturated fatty acids (MUFAs), particularly from olive oil, has been associated with lower cancer risk. Similarly, the replacement of animal MUFAs with plant MUFAs decreased cancer mortality. The impact of polyunsaturated fatty acids (PUFAs) on cancer risk depends on the ratio between ω-6 and ω-3 PUFAs. In vivo data showed stimulatory effects of ω-6 PUFAs on tumour growth while ω-3 PUFAs were protective, but the results of human studies were not as promising as indicated in preclinical reports. As for trans FAs (TFAs), experimental data mostly showed opposite effects of industrially produced and natural TFAs, with the latter being protective against cancer progression, but human data are mixed, and no clear conclusion can be made. Further studies are warranted to establish the role of FAs in the control of cell growth in order to find an effective strategy for cancer prevention/treatment.
Highlights
A high-fat diet (HFD) has been regarded as detrimental for health, but in many cases, it is the obesity as a consequence of excess caloric intake that is in the background of various pathologies, including diabetes, cardiovascular diseases, and cancer [1]
As the human data show, a mere cut on fat intake does not have an impact on cancer risk; it is the fatty acids (FAs) spectrum of dietary fat that is significant
The protective effects of ω-3 polyunsaturated fatty acids (PUFAs) against malignant transformation in human studies were not as eminent as indicated in preclinical reports; one of the reasons might be that the level of ω-3 PUFAs in human diets did not reach the doses effective in animal models and that their beneficial effects might be counteracted by ω-6 PUFAs
Summary
A high-fat diet (HFD) has been regarded as detrimental for health, but in many cases, it is the obesity as a consequence of excess caloric intake that is in the background of various pathologies, including diabetes, cardiovascular diseases, and cancer [1]. Changes of the gut microbiota induced by long-term administration of HFD to mice were associated with increased intestinal ROS production and oxidative stress [15], which play a significant role in cancer initiation and progression [16] (Figure 1). The disruption of the gut–liver axis by dietary fat plays an important role in the development and progression of portal hypertension, chronic liver disease, and cirrhosis, with the latter being a pre-cancer state [40] (Figure 1) Both animal and human reports focus almost exclusively on the bacterial component of the microbiome, but apart from the bacteria, the human microbiome hosts viruses, fungi, and archaea that can all be altered in disease states [41]. Complex interactions between neoplasm growth and sympathetic nervous system were reviewed elsewhere in detail [75,79,80]
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