Health Benefits Of Tomatoes

Introduction

Tomato is a fleshy vegetable that is  highly nutritive and offers  several health benefits such as improving immune response, bone strength and cognitive function, and protective actions against inflammation, cancer, neurodegenerative diseases, cardiovascular diseases, and bowel diseases.^2,5 Tomatoes can be consumed raw (fresh), cooked, or as processed products such as juice, soup, sauce, and puree.^{1, 3} Tomatoes largely consist of water (>90%).^2,13 However, they are also rich in carotenoids, proteins, vitamins (A, B, C and E), minerals, iron, folate, carbohydrates, essential amino acids, monounsaturated fatty acids and phytosterols.^{1, 2, 4, 7} The environmental conditions in which tomatoes grow, such as, but not limited to, temperature, light intensity and water availability, can affect the quality of the nutrients.^2,4,6 The most important nutritive component are the carotenoids.³ The main carotenoid is lycopene, which gives  tomatoes the characteristic red colour.¹ In addition, it is the antioxidant properties of lycopene that give tomatoes their protective action³ The second main carotenoid is beta-Carotene which gives the orange colour^.4 Tomatoes can also be yellow, pink, purple, black and even white colour.¹⁴

About tomatoes

Health benefits of tomatoes

The rich supply of nutrients in tomatoes gives them a diverse range of health benefits though the predominant effects are antioxidant, anti-inflammatory, and anticancer^.6 

Cancer

In cancer, the cells become altered (mutated), grow uncontrollably and may spread to other areas of the body. The anticancer effects of tomatoes  are due to two important carotenoids (Lycopene and β-carotene). These carotenoids prevent the oxidative damage of DNA and proteins^.2 Lycopene works by selectively suppressing the growth and inducing apoptosis (cell death) of the abnormal cancer cells.⁸ Lycopene also has specific actions against certain types of cancers. Lycopene inhibits the proliferation of HT-29 colon cancer cells and oestrogen-dependent/-independent breast cancer cells.² In pre-menopausal women, insulin-like growth factor 1 (IGF-1) is an important factor in developing  breast cancer. Lycopene mitigates this risk by stimulating the production of a protein that binds to IGF-1, thereby lowering the blood concentration.⁸ Furthermore, tomato peel and seeds are composed of 60% dietary fibre which is metabolised by intestinal microbiota to form short-chain fatty acids that prevent colon cancer by blocking their source of energy.²

Cardiovascular diseases

Tomato reduces the blood concentration of plasma cholesterol and triglycerides while increasing plasma high-density lipoprotein (HDL) cholesterol and interleukin-10 concentrations. In addition, the antioxidants in tomatoes (lycopene, beta-carotene, and vitamin C) protect vascular cells and lipoproteins from oxidation, inhibit platelet aggregation and prevent inflammatory changes and apoptosis (cell death).²

Neurodegenerative diseases

Examples are Alzheimer’s disease, Parkinson’s disease, depression, cerebral ischemia (stroke) and epilepsy. The lipophilic (fat-soluble ) nature of lycopene allows it to easily cross the blood-brain barrier where it can exert its neuroprotective effects. These includeimproving cognitive and memory function,  preventing proteinopathies (an umbrella term for neurodegenerative disorders that are characterized by the accumulation of specific proteins within neurons or in the brain parenchyma such as Alzheimer's disease and Parkinson's disease¹⁰), neuroinflammation, apoptosis, cerebral edema (swelling), and synaptic dysfunction.^{9, 11}

Gut diseases

The high fibre content in tomato skin and seeds is a rich prebiotic that increases the diversity of gut microbes.² Prebiotics are carbohydrates that are tough to digest. Probiotics allow us to easily digest carbohydrates. In order words, the fibre is nutritive for beneficial intestinal bacteria (e.g. Lactobacillus rhamnosus and Bifidobacterium bifidum) while inhibiting “bad” bacteria (e.g. Clostridium difficile), fungi and viruses, thus modulating gut microbiome.¹² Studies have also shown beneficial effects against metabolic syndrome and obesity.³

Others

In diabetes, studies have shown that lycopene exerts hypoglycaemic effects by increasing serum insulin levels, and protecting the kidneys by reducing angiotensin converting enzyme (ACE) activity, regulating connecting tissue growth factor and enhancing antioxidant activities.¹ In the immune system, beta carotene and vitamin C increase the concentration of plasma lymphocytes which help in the fight against infection; and in recovering from exercises, the antioxidants scavenge for free radicals thus inhibiting the reactive oxygen species (ROS) which can damage the cells.¹⁴ For vision, the vitamin may reduce the risk of macular degeneration while β-Carotene can be converted into retinol, a compound that is essential for vision.³ In the skin, beta-carotene and lycopene helps protect against UV rays from the sun.²

Nutrients we can get from tomatoes

Tomatoes are an important dietary source of nutrients and bioactive compounds. The tomato fruit structure consists of a pericarp which has three layers the exocarp which is the outermost layer and is the richest in antioxidants; the mesocarp which is the middle layer and is rich in minerals and water; and the endocarp which is the inner layer and contains the seeds which are rich in vitamin C. The seeds also contain steroidal saponins called lycoperosides which are believed to exert anti-inflammatory effects.²

Fresh raw tomato contains 18 kcal energy per 100g. This consists of >90% water. The macronutrients composition in this serving are 3.89 g of carbohydrate (consisting of 2.7 g sugar and 1.2 g of dietary fibre, with the rest being complex carbohydrate), 0.9 g of protein and 0.2 g of fat^14,18 The mineral constitution are potassium (237mg), phosphorus (24mg), magnesium (11mg), calcium (10mg), sodium (5mg), iron (0.27mg), zinc (0.17mg), manganese (0.114mg) and copper (0.059mg) while antioxidants and vitamins include vitamin C (<21mg), lycopene (<14.6mg), phenolic acids (<4.9mg), vitamin E (<1.8MG) and beta-carotene (<1.1mg). The antioxidants in tomato are classified as hydrophilic (meaning water soluble. This is about 83% of total antioxidant activity. Examples include soluble phenolic compounds and vitamin C) or lipophilic (meaning fat soluble. Examples are carotenoids, vitamin E, and lipophilic phenols. This is about 17% of total antioxidant activity).^1,3,16 The soluble and insoluble dietary fibers (cellulose, hemicelluloses and pectins) are resistant to intestinal digestion in the large intestine and are believed to ameliorate metabolic disorders, bowel diseases, cancer and cardiovascular diseases.¹

Tomato is a perishable fruit, and is usually preserved in other forms such as dried canned juice or soup.¹³ In this processed forms, additives like sugar and salt are included, with studies showing lower water content and higher fat soluble content, fibre, vitamin C and protein levels^13,14,16 However, these nutritional composition is influenced by the environmental conditions, cultivation and harvesting methods and cold storage.^{1,13,15,16,17}

How to include tomatoes in our diet?

Tomatoes are richly nutritive. In addition, tomatoes are naturally high in fibre and low in energy (calories), and so help maintain a healthier weight. Tomatoes can be eaten fresh, but they are also versatile in how they can be used in different meals. For example, they can be used to make sandwiches and salad. They can be blended alone or mixed with other vegetables and fruits to make smoothie, however this releases the sugar hence increasing the content and removes the fibres so it is advised to drink at most 150ml. Tomatoes can be included with onion, peppers, and sweetcorn in making scrambled eggs. Another option is in making sauces which can be used in meals like spaghetti.

How much is enough?

Side effects and how much to consume

In the UK, it is recommended to eat at least 5 portions of a variety of fruit and vegetables every day. An adult portion is 80g of fresh, canned, or frozen fruit and vegetables or 30g of dried fruit.¹⁴ If the fruits and vegetables is made into juice, puree, or smoothies, then the advice is to drink no more than 150ml a day, the equivalent of a small glass.^{13, 14} The NHS defines smoothies as any drink made up of any combination of vegetable  or fruit juice, purée, or all the edible pulped vegetable or fruit. 1 medium tomato is classified as a portion.¹³

Despite the healthy benefits of tomatoes, excessive consumption can result in symptoms such as heartburn (due to the acidic contents including citrate and malic acid), anaphylactic reactions (due to the histamine content), urinary problems (such as kidney stones due to the calcium and oxalate content), migraines, lycopenodermia (an orange or red discolouration of the skin due to the lycopene content) and irritable bowel syndrome (due to the indigestible seeds and skin).²,⁶

Summary

Tomato is a rich dietary source of micronutrients and bioactive compounds, including minerals, vitamins (A, C, E, K), iron, folate, essential amino acids (leucine, threonine, valine, histidine, lysine, arginine), carotenoids (lycopene and β-carotenoids) and phytosterols (β-sitosterol, campesterol and stigmasterol). The chemical composition is affected by the environment, genetics and cultural practices.³ Tomatoes can be eaten raw, cooked or processed (puree, sauce or juice). Lycopene is the main dietary carotenoid and is the most important nutritional component of tomatoes. Tomatoes have a diverse range of health benefits, such as improving skin health, bone strength, exercise recovery, and immune response and protective effects from cancer, cardiovascular, neurodegenerative and intestinal diseases² The main mechanism of action is antioxidation which it achieves by inhibiting reactive oxygen species (free radicals) and reducing oxidative damage.¹ The nutrients that provide this antioxidant property are vitamin C, carotenoids (beta-carotene and lycopene), and phenolic compounds (flavonoids, hydroxycinnamic acid, chlorogenic, homovanillic acid, and ferulic acid).²