Colorectal Cancer in Africa: Causes, Dietary Intervention, and Lifestyle Change

Cancer could be described as an uninhibited, uncontrolled growth of abnormal cells spreading within the tissues, organs, or systems of the body. Risk factors associated with cancers could be peripheral if regularly exposed to hazardous chemicals, radiation, and infectious diseases; or viscerally when cell growth abnormalities are associated with hormonal alterations, gene mutations and immune state ⁶. Physiological state of individuals, age and hereditary factors could also influence whether one is likely to have cancer.

Cancers are of various types which affect organs and tissues such as colon, breast, prostate, bone, blood etc. ⁷. For CRC, the growth and dispersal of neoplastic alterations are evident and characterized by tumoural growth in the bowel regions of the body ⁸. Obviously, significant alterations of the sequence of DNA (mutations) represent this initial event ⁸. Though the prevalence of colon cancer varies from country to country, amongst numerous factors with reference to socio- class, individuals with low standards of living especially in the areas of nutrition and hygiene are more likely associated with increased risk of colon cancer. Among the important risk factors of this cancer include family or personal history of adenomatous polyps, presence of diseases such as diabetes mellitus, obesity, inflammatory bowel diseases (IBD), and history of Lynch syndrome ⁹. Racial or ethnic background also plays a role as a high record of mortality and morbidity due to this disease have been documented in black Americans and Jews of Ashkenazi descent ⁹. In spite of facts showing that genetic and environmental factors perform significant roles in the oncogenesis of the colon, extended studies had suggested that dietary interventions might be utilized for fundamental and defensive roles in the body to deter the development of colon carcinoma ¹⁰.

Globally, colorectal cancer is ranked third most common among cancers after breast and lung cancers ¹¹. The screening process has shown that it remains the most avoidable major cancer. There appears to be a complex genetic relationship in the component of the initiation, promotion, and progression of colorectal cancer, which poses a risk of its development ⁶. Presently, over 1.2 million people are diagnosed annually, though rarely seen in individuals under the age of 40, it usually occurs in people at 60 and over.

Despite the economics linked with the screening and the availability of certified screening tools, the prevalence rate of the disease is expected to rise to 33.5% in 2020. Globally, the economic affliction posed by colon cancer is overwhelming and stated to be in surplus of $33,000,000,000 per annum ^{12, 13}. While this disease tends to ravage the African race, it is imperative that recommended screenings centres and equipment should be provided most especially in the rural areas. Global Statistics has shown that cancer of the colon is higher in Western countries than in Africa. In Black Americans, an estimated 6.5% of people in the U.S, while 0.4% occur with people in Sub-Saharan Africa.

Diet plays a key role in exposing humans to environmental carcinogens and anti-carcinogens, consequently mitigating or aiding in the development of various cancers ¹⁴. African diet has demonstrated a protective role against colon cancer due to the high fibre content of the diet ¹⁵. Dietary fibre is the major component in African dishes that offers protection against colon cancer as it clearly differentiates the African diet from the Western diet that is characterized by consumption of more fatty foods and refined products. A study reported that switching the diet of African American patients to the traditional African diet influenced gut bacteria in such manner that could prevent cancer development ¹⁶.

Makki et al. ¹⁷ reported that the traditional African diet plays a protective role against gut tumor promoters such as Carcinoma embryonic antigen (CEA), Cyclooxygenase-2 (Cox-2), A33-transmembrane glycoprotein member of the immunoglobulin superfamily, Telomere/telomerase-TERT, Urokinase-type plasminogen activator receptor (uPAR) gene, Fibroblast growth factor 18 (FGF18), endothelial cell type-specific tyrosine kinase domain-containing receptor (KDR) ¹⁸ modifies colonic bacterial fermentation and alters gut motility. Dietary fiber also binds bile acids in the gut and prevents the conversion of primary to secondary bile acids. The fermentation of fiber by colon bacteria generates volatile short chain fatty acid (SCFA) that induces apoptosis and inhibits neoplastic tumor development. Dietary fiber also lessens the risk of colon cancer by reducing nitric oxide, inflammatory markers, insulin resistance and increasing fecal bulk, lessening the potential interactions between fecal mutagens and colon mucosa ¹⁹. Several animal experiments, clinical trials and epidemiological studies have shown reduced risk of colorectal cancer with increased consumption of dietary fiber ²⁰. However, it has been observed that the type of fiber consumed determines the protective effect as many studies have found little to no protective effect with cereal fiber and a significant protective effect with vegetable and fruit fiber.

In Africa, vegetables being an important part of the traditional diet are consumed daily by the rural populations due to their accessibility, affordability, and availability. They consist of dark green leafy vegetables (amaranth, spinach, jute leaves, baobab leaves, water leaves, cassava leaves, cowpea leaves, pumpkin leaves), root vegetables (onions, garlics, carrot, ginger, beet roots) and cruciferous vegetables (turnips, cabbage, lettuce, broccoli). Vegetables are rich sources of retinol, ascorbic acid, folate, and minerals such as iron and magnesium ⁴¹. Retinol and ascorbic acid are strong antioxidants and anti-tumorigenic. Folates stabilize tumor suppressor genes and prevent increase in cell proliferation ⁴². The phytochemical content of vegetables also confers its protective role against colorectal cancer (see Table 1). Major phytochemicals found in vegetables such as flavonoids, terpenoid, alkaloids and phenolic compounds are potent inhibitors of reactive oxygen species, are cytotoxic and prevent the alteration of DNA. Cruciferous vegetables have been reported to induce phase I and II metabolism 2-amino-1-methyl-6-phenylimidazo^{4, 5}pyridine (PhIP), decreasing the occurrence of colon cancer ⁴³. Allium vegetables (onions, garlic) serve as an essential flavoring base in most African soups and stews. A 29 months hospital-based case-control study that consecutively recruited 833 cases of CRC and matched them to 833 controls by age not more than 2.5 years of difference, reported that consuming high total allium vegetables decreased the chances of colorectal cancer in adults by 79% ⁴⁴. This was attributed to their disulphide content that suppresses cell division in human colon cancer cell lines. Vegetables are also rich sources of dietary fiber. Sufficient intake of both green and yellow vegetables provides insoluble dietary fibre that serves as a protective factor for these cancer types ⁴⁵.

Fruits are an important part of the African traditional diet. Commonly consumed fruits in Africa include vegetable fruits such as tomatoes, pepper, cucumbers, and eggplant. The regular fruits include avocado, baobab fruit, citrus fruits, guava, mango, pawpaw, pineapple, watermelon, passion fruit, banana, and jackfruit. Most of which are genetically unmodified. Although, studies have not confirmed any association between genetically modified foods and cancer, despite the risks and concerns associated with GMO foods ⁴⁶. Fruits are good sources of dietary fiber, vitamins (A, B, C and E), minerals (potassium, magnesium, phosphorus, selenium) and phytochemicals (flavonoids, phenols). Ascorbic acid, a major component in citrus fruits, is associated with tumor regression in advanced diseases and chemo sensitizing colorectal cancer cells ⁴⁷. Other antioxidative vitamins in fruits such as retinol and tocopherol reduce the toxic effect of reactive oxygen species (ROS) in cancer causation and they decrease epithelial cell proliferation ⁴⁸. Fruits are also rich in minerals such as phosphorus, selenium, potassium, zinc, and magnesium that offer a protective role for colorectal cancer by increasing the expression of antioxidant enzymes and boosting the immune response. The stew base in most African countries are spicy fruits such as sweet pepper and habanero pepper which are rich in antioxidants (See table 1). Capsaicin, a major phytochemical in peppers was reported to possess cytotoxic, anti-proliferative and pro-apoptotic effects against colo 205 colorectal cancer cells in an in vitro study ⁴⁹. Lu et al. ⁴⁹ also reported that capsaicin inhibited tumor growth in mice with colo 205 tumor xenografts.

The main staples in Africa include roots and tubers (cassava, yam, potato, cocoyam, sweet potato), cereals (Sorghum, corn, millet, rice), and bananas (Plantain, green banana). Staple crops generally are rich in polyphenols, vitamins, and minerals with cancer-preventive properties. These food crops serve as the main energy source in African diet. Root and tubers are rich sources of non-digestible carbohydrates (NDCs) such as fiber and resistant starch. NDC undergoes anaerobic fermentation to produce short chain fatty acids: acetic acid, propionic acid and butyric acid which lower the pH of the intestinal lumen. The lowered PH levels favors the establishment of healthy gut microbiota to produce short chain fatty acid that alters preneoplastic lesions, suppress mutations and bind potential carcinogens in the colon ⁵⁰. Short chain fatty acids also directly interact with cells in the gut to elicit immunologic effects such as the regulation of T helper cells, lymphoid cells, cytotoxic T cells and B cells to improve host immunity, suppress inflammation and allergic responses ⁵¹. The risk of colon cancer is reduced by about 40% with high intake of NDC from staples ⁵². Grains form the bulk of staples and whole grains are majorly consumed in the rural parts compared to the urban centers. Tocopherol and selenium which are richly present in whole grains are strong antioxidants with colon cancer preventive properties. The consumption of whole grains was reported to significantly reduce the risk of colorectal cancer by 11% ⁵³.  Table 2

Legumes (soybean, pigeon pea, bambara nut, groundnut, beans) are important protein source in the African diet. Asides being rich sources of proteins, they also contain phytoestrogens. Genistein, a phytoestrogen in soy was reported to inhibit proliferation of HT-29 colon cancer cells by mediating a cancer promoter protein, EGF ⁵⁴. Flavonoids in leguminous foods are involved in the regulation of cellular proliferation and apoptosis in the colon. The high folate content of legumes is also responsible for the decrease in the risk of colon cancer. Higher consumption of legumes especially from soy has been reported to reduce the incidence of colorectal cancer in Asians ⁵⁵.  High intake of meat has been associated with an elevated risk of colorectal cancer and substituting legumes as a source of protein may inversely reduce the risk of colorectal cancer.

Due to the high cost of meat and fats in many parts of Africa, the consumption is typically low. Africa obtains an average of 18% of total food energy from dietary fat ⁶². Much of the fat content in the traditional diets comes from plant oils that are rich in monounsaturated fats such groundnut, palm kernel, sesame, olive, sunflower, soybean, and coconut oils. The lower consumption of animal protein and fat in the traditional African diet may have contributed to the low incidence and risk of colon cancer among the African populace. The lesser consumption of saturated fats in the western diet is linked with a decrease in risk of developing colon cancer as saturated fat contributes to enhanced tumor formation ⁶³. An in-vivo examination carried out by Garcia-Villatoro et al. ⁶⁴ showed that western diets are directly associated with colorectal cancer. The study administered mice with high-fat diet to simulate the mixed lipid composition in the average western diet and it was indicated that cryptic cell proliferation and colon mass multiplicity was promoted at the premalignant colon cancer lesion. The study also showed β-catenin expression and nuclear localization in actively proliferating cells in colon masses.

In addition, meat processing methods that applies high temperature that are peculiar in the west have also been linked with colon cancer risks. Among the first pyrolysis mutagens to be isolated and identified are the pyridoimidazole, pyridoindole and the quino xalines, which are major mutagens found in high heat over processed beef ⁶⁵. A study has reported that South Africans who consumed a typical Westernized diet rich in saturated animal fat, cholesterol and animal protein had high blood lipid levels and were at increased susceptibility to colon cancer ¹⁹. A diet with high fiber and low animal products is advantageous to colonic metabolism. The low sulfur amino acid content permits the overgrowth of methanogenic bacteria, which convert maldigested carbohydrate into SCFA ⁶⁶. The reason ulcerative colitis and other noninfective colonic diseases are so rare in Africans is related to low animal protein diet and consequent low colonic sulfite production.

Some spices such as turmeric, clove and red pepper are rich in antioxidant properties, hence can regulate cellular oxidative stress. Likewise, they have the capability of stopping the reactive oxygen species from being produced and disrupting the signal transduction pathways.  These spices possess potential therapeutic effects in the management and treatment of cancers due to their anti-inflammatory, antioxidant, and immunomodulatory effects ⁶⁷.

Curcumin, an important constituent of turmeric, possesses anti-tumor, anti-inflammatory and antioxidant properties ⁶⁸. Curcumin has been reported in several studies to inhibit cancer promoting signal pathways inducing apoptosis, inhibiting proliferation and hindering cell growth of cancer cells including colorectal cancer cells ⁶⁹. According to Yoon et al.⁷⁰ curcumin exhibits its anti-cancer effect at a dosage of 3,600mg/day. 

Colon cancer has increased in Africa with the integration of the western diet into the traditional African diet characterized by the consumption of more processed foods ⁷¹.  These ultra- processed foods include baked products, sugary beverages, sweets, sugary cereals, and fizzy drinks. These foods have been easily introduced into the African traditional diet because of their convenience and ‘ready-to-eat’ nature, hence the classic term ‘fast foods’ ⁷².

The influx of small-scale food enterprises comprising fast-food, drinks, desserts, cakes, and biscuit enterprises in modern times has significantly increased the consumption of ultra-processed food. Most of these processed foods have low nutritional value and are packed in unhealthy saturated fats, sugar, preservatives, and flavor enhancers. These components added to processed foods makes their consumption addictive. Moreso, these unhealthy components of processed foods are associated with an increase in risk of developing colon cancer as heavy consumption of sugary processed products in adolescents and adulthood, on a daily basis, doubles the risk of developing colon cancer before the age of 50 ⁷³. Sugar promotes cancerous tumors as the growth of polyps depends on the availability of glucose and fructose. Saturated fats cause an imbalance in intestinal bile acids and trigger inflammatory factors that promote tumor development ⁷⁴. Sodium nitrites, a common food additive found in processed meat products are metabolized into cancer causing N-nitroso compounds. Monosodium glutamates have been reported to increase the susceptibility of experimental animals to colon cancer ⁷⁵.

Processed foods are also indirectly linked with an increase in risk of cancer by elevating factors responsible for colon cancer such as obesity and diabetes ⁷⁶. Chen et al. ⁷⁷ reported that an exponential increase in consumption of processed foods increased the risk of cancer by 12%. The shift in the consumption of less whole grains to the consumption of refined grains has increased in the African traditional diet. Refined grains are often preferred for their appearance, texture, and taste but they have low nutritional value. Rice and wheat are the major examples of staple whole grains in Africa that are majorly refined.  Refined grains have low fiber, mineral, vitamins, and phytochemicals (polyphenols and flavonoids) with antioxidant properties that reduce cancer. Refined grains are now fortified with the lost nutrients but the health promoting phytochemicals that are anti-cancerous cannot be replaced. High intake of refined grains has also been associated with the increase in incidence of gastric and colon cancer ⁷⁸.

There is an increase in availability of processed meat products such as sausage, ham, bacon, and cheese in Africa. The integration of these processed meat products in the traditional African diet also increases the risk of colon cancer. Moreover, the increased production of locally available processed meat products such as spiced beef strips, smoked and fried meat chunks have increased the consumption of red meat in African countries as most of these products are increasingly sold and purchased. The processing methods of meat in Africa is also of serious concern.  In most households, meat is often deep fried in used oils.  Moreover, the grilling and smoking method of meat products to produce barbecued products is common in various food-bar outlets in Africa. The fried and barbecued meats are preferable for their flavor and aroma, however the high temperature processing method used accompanied with the presence of smoke (in barbecued meat products) generates heterocyclic amines (HCAs) that increases susceptibility to colon cancer ⁷⁹. Processing methods used in meat preparation such as high temperature (120-230⁰C), smoking and inclusion of preservatives produce harmful carcinogenic substances such as heterocyclic amines, polycyclic hydrocarbons, N-nitroso compounds, and acrylamide. Increased meat consumption also causes heme iron overload that encourages cell growth and proliferation by generating reactive oxygen species, inducing oxidative stress, and catalyzing processes involving the formation of nitroso compounds ⁸⁰.

Colorectal cancer (CRC) has been reported as the third most common cancer. From the record of World Health Organization GLOBOCAN, nearly 1.2 million people were diagnosed with CRC and 608,000 deaths were recorded in 2008 ⁸¹. Over the years, the occurrence of CRC is considered rare among native Africans compared to the modern countries but with the increase in urbanization and industrialization, there has been a recorded rise in the incidence of colorectal cancer ^{82, 83} among the African populace. 

The incidence of CRC in some West African countries was less than 0.003% about 40-50 years ago ⁴. However, between 1954 and 2007, the incidence of colorectal cancer has increased by 7% and 87.42% in Nigeria and Ghana, respectively. 

As reported in sub-Saharan Africa, CRC represents the fifth most common malignancy ⁸⁴. Studies have shown changes in diet and lifestyle play a vital role in the early prevention of CRC ⁸⁵.

This increase in trends of CRC could be linked to etiological factors such as increase in consumption of alcohols, obesity, lack of physical activity, tobacco usage, highly refined diets low in fiber, carbonated drinks, fast foods.  Alimentary factors are also linked to high CRC as observed in countries that consume high amounts of red meat and processed meat products.

The diets of average African are mostly carbohydrate based and the starches and polysaccharide (non –starch) in the diets are fermented by the bacteria in the colon into colon friendly acids such as acetic acid, propionic acid and butyric acid which are associated with low colon cancer risk.

The plant-based diets have been reported to be protective and this may be partly due to absence of meats which when cooked or processed may produce carcinogens and saturated acids which are injurious to health. Additionally, plant-based diets are a rich source of vitamins, phytochemicals and fibre which offer several health benefits like weight loss or weight maintenance which invariably reduce the risk of obesity which has been linked to CRC.

Likewise, there should be a drastic reduction in consumption of red and processed meats as they contain high cholesterol, saturated fats leading to high levels of cholesterol in the serum and triglycerides associated with high CRC risk. Hence, a healthier diet of fruits, vegetables and whole grains combined with increased physical activities which result in healthy body weight should be adopted as a lifestyle as it is associated with being CRC free ⁸⁶.

Physical activity has been linked to reduce not only CRC but other forms of cancer while inactive lifestyle may cause a rise in the incidence of CRC.  Physical activity has been said to not only reduce colon cancer risk but help in maintaining energy balance, enhance the immune system, regulate insulin levels, alter prostaglandin levels and enhance movement of the contents in the colon through the gut ⁸⁷.

It has been stated that alcohol increases the chance of CRC by 60%, this is because its metabolism produces acetaldehyde and metabolites which promote carcinogenesis via its various mechanisms ^{88, 89}. Alcohol consumption can lead to malnutrition deficiencies of vitamins (such as B6 and B12), DNA synthesis and methylation ⁹⁰.