Dietary restriction (or DR) is the reduction of a specific nutrient or overall nutrient intake without causing malnutrition. DR methods have been shown to slow ageing in various animal models, although whether dietary restriction practices like fasting and calorie restriction can slow ageing in humans is not known.
One of the most immediately noticeable aspects of human ageing is the degradation of skin quality and the formation of wrinkles. However, skin ageing is not just cosmetic: aged skin is more fragile, takes longer to heal, and is more susceptible to a variety of skin diseases including cancers. In this article, we ask whether there is any evidence that DR can slow skin ageing.
To understand how skin ages, we must first outline its basic structure. Skin is composed of three layers: the outer layer or epidermis, which creates a tough waterproof barrier; the keratin-rich middle layer or dermis, which contains connective tissue, hair follicles and sweat glands and provides elasticity; and the inner layer or hypodermis, which contains connective tissue and fat, acting as both insulation and as an energy store.
Wrinkles occur primarily due to changes in the dermis. Collagen and elastin are structural molecules within the dermis that hold cells together and grant the skin most of its firmness and elasticity. Production of these molecules declines with age, causing the skin to lose its elastic properties, becoming more brittle and prone to wrinkling and sagging. Additionally, the transfer of moisture from the dermis to the epidermis slows with age, while sebaceous (oil) glands and fat cells begin to shrink. These changes make the skin drier, duller and thinner.
Skin ageing is thought to be driven by free radicals, which are molecules that can damage other molecules like proteins and DNA by ‘stealing’ their electrons. Free radicals are a natural product of normal cellular processes, but their production increases with age, while the body’s ability to neutralise them declines. Free radicals can also be generated in response to environmental factors such as diet, exposure to cigarette smoke, and direct damage to the skin (due to ultraviolet radiation, for example).
Another driver of skin ageing is glucose. Glucose molecules can react with proteins or lipids in a process called glycation to form advanced glycation end products, or A.G.Es. A.G.Es can then react with structural proteins in the skin in order to link them together, resulting in a reduction in elasticity. Glycation is also promoted by free radicals and by ultraviolet radiation.
Last but not least, damage to the DNA of cells within the skin is an important factor in skin ageing, as it leads to an increased production of free radicals, defective protein production and an increased risk of developing skin cancers. DNA damage also leads to the death of stem cells within the skin, which is thought to be involved in the ageing process. Stem cells are capable of dividing and giving rise to multiple types of cell, and are therefore essential for tissue maintenance and repair. The main source of DNA damage is usually ultraviolet radiation from the sun.
DR practices have been demonstrated to have numerous health benefits including protection against inflammation, reactive oxygen species and DNA damage. Given the involvement of these processes in ageing skin, it is not unreasonable to expect DR to have an effect on skin ageing.
The effects of dietary restriction on the skin have primarily been studied in animal models. Overall, they point to a beneficial effect of DR for skin health and ageing. One study reported that long term 60% calorie restriction lowered the rate of skin protein glycation – the cross linking of proteins we mentioned earlier. Glycation is considered to be one of the primary drivers of skin ageing. The fact that calorie restriction opposes this process is therefore a good indication that DR has the potential to slow skin ageing.
DR has been shown to promote the activity of macrophages, the ‘janitors’ of the immune system that are responsible for clearing up debris from sites of injury. Studies suggest that this increase in macrophage activity may play a role in promoting skin healing in rodents subjected to DR. However, not all studies are in agreement, with some research suggesting that calorie restriction actually slows healing. DR has also been found to promote the renewal of stem cells, though its effects on stem cells in the skin specifically are relatively under investigated.
Evidence suggests dietary restriction may inhibit the progression of various skin diseases including psoriasis, acne, and certain skin cancers. In cultured melanoma cells for example, nutrient deprivation was found to improve the effectiveness of chemotherapy.
Unfortunately, the effects of dietary restriction on the skin, and on health more generally, are less well studied in humans. We understand the processes behind skin ageing relatively well, and evidence from animal models suggests that dietary restriction should slow these processes. However, extensive research is required before we can say with confidence whether dietary restriction effects human skin ageing.
Why Does Your Skin Age? https://sites.dartmouth.edu/dujs/2013/01/28/why-does-your-skin-age/#:~:text=The%20collagen%20and%20elastin%20fibers%20break%2C%20thicken%2C%20stiffen%2C%20clump,glands%20have%20decreased%20in%20size.
Fasting and Its Impact on Skin Anatomy, Physiology, and Physiopathology: A Comprehensive Review of the Literature: https://dx.doi.org/10.3390%2Fnu11020249
Fasting boosts sensitivity of human skin melanoma to cisplatin-induced cell death: https://doi.org/10.1016/j.bbrc.2016.09.149
Shedding Light on the Effects of Calorie Restriction and Its Mimetics on Skin Biology: https://dx.doi.org/10.3390%2Fnu12051529
Diet in dermatology: Part I. Atopic dermatitis, acne, and nonmelanoma skin cancer: https://doi.org/10.1016/j.jaad.2014.06.015
Effect of calorie restriction and refeeding on skin wound healing in the rat: https://doi.org/10.1007/s11357-011-9321-6
Influence of Short-term, Repeated Fasting on the Skin Wound Healing of Female Mice: https://www.researchgate.net/profile/Farzad-Hayati/publication/265204934_Influence_of_Short-term_Repeated_Fasting_on_the_Skin_Wound_Healing_of_Female_Mice/links/5474f3a30cf2778985acf25c/Influence-of-Short-term-Repeated-Fasting-on-the-Skin-Wound-Healing-of-Female-Mice.pdf
Prolonged Fasting Reduces IGF-1/PKA to Promote Hematopoietic-Stem-Cell-Based Regeneration and Reverse Immunosuppression: https://doi.org/10.1016/j.stem.2014.04.014
Caloric restriction decreases age-dependent accumulation of the glycoxidation products, N epsilon-(carboxymethyl)lysine and pentosidine, in rat skin collagen: https://doi.org/10.1093/gerona/50a.6.b337