Cancer is one of the leading causes of death throughout the world: there were an estimated 14.1 million cancer cases around the world in 2012, of these 7.4 million cases were in men and 6.7 million in women. This number is expected to increase to 24 million by 2035 (http://gco.iarc.fr/) (Figure 1) Cancer is a widespread disease that affects a large majority of the population either directly, because they develop it, or indirectly, because they know or are related to someone with the disease. Cancer can form in almost any organ or area of the body, being a major and increasing health concern [1,2]. Cancer growth and progression it is shown schematically in (Figure 2).

Figure 1: Estimated number of incident cases, both sexes, worldwide (top 10 cancer sites) in 2012.

Figure 2: Cancer growth and progression.

In the 80s, Doll and Peto published a review regarding factors known (at that time) to affect cancer risk [3]. The main cancer risk factors described by Doll and Peto are: tobacco, diet and nutrition, occupation and infection. Doll and Peto stated that epidemiological evidence regarding diet and cancer was largely indirect. They made an estimate by cancer site and they indicated that “perhaps” 90% of stomach and colorectal cancers, 50% of pancreas and breast cancers, 20% of lung cancers and 10% of other cancers may be diet related [3,4].

In the last decades, several studies were performed in order to explore and analyze associations between diet and risk of cancer. World Cancer Research Fund and American Institute for Cancer Research [5], World Health Organization [6], U.S. Department of Health and Human Services and U.S. Department of Agriculture [7], American Diabetes Association [8], etc. published several comprehensive reports related to diet and cancer.

In order to explore associations between dietary patterns and risk of cancer index-based approaches were increasingly used. The commonly used approach is Healthy Eating Index (HEI), developed based on the Dietary Guidelines for Americans recommendations. As shown is several research papers [9-16], higher HEI scores are related to lower risk of cancers.

According to Solbak et al. [17] after assessing dietary quality in a subset of participants in Alberta’s Tomorrow Project (ATP), the data suggest that higher quality diets may be protective against cancer in men, but not women.

Nutraceuticals, for example, are bioactive molecules found in foods, like curcumin, resveratrol, genistein, quercitin, lycopene, etc. (Figure 3). They have been shown to exert anticancer activity [17]. The main factors limiting the oral bioavailability of anticancer nutraceutical are: bioaccesibility (liberation from foods and solubilization in gastrointestinal tract fluids), absorption (transport through mucus layer and into epithelium cells) and transformation (chemical or biochemical modifications). They are schematically presented in (Figure 4) [17].

Figure 3: Chemical structure of bioactive molecules (nutraceuticals) found in foods.

Figure 4: Factors limiting the bioavailability of nutraceuticals.

Based on the mentioned aspects, functional foods must be carefully designed to contain nutraceuticals themselves or to boost the bioavailability of nutraceuticals in other foods. Further research is still needed to demonstrate the efficacy of nutraceuticals.

Several studies have also shown how the antioxidant and anti-inflammatory effect of honey can prevent the initiation of cancer, although the full mechanism is not well defined yet. Honey is composed of various sugars, flavonoids, phenolic acids, enzymes, amino acids, proteins and minerals. Its composition varies according to floral sources and origin [18]. Honey shows antiproliferative activity, both in vitro and in vivo, inducing apoptosis and cell cycle arrest. Furthermore, honey improves the activity of anticancer drugs other than ameliorating life quality of patients undergoing chemotherapy [19-27].

On the opposite site, food contamination by mycotoxins, among other chemical contaminants, has been recognized as a public health threat [28,29] and mycotoxins have been included as priority food contaminants by World Health Organization (WHO) [30]. Aflatoxin B1, Aflatoxin M1, Ochratoxin and Deoxynivalenol are potent toxic mycotoxins [31], Aflatoxin B1 being classified by International Agency for Research on Cancer (IARC) as “carcinogenic to humans” [32]. Mycotoxins occur in highly consumed foods such as cereals, milk, dairy products, fruits, coffee, wine, beer [33]. Mycotoxins have been ranked as “the most important chronic dietary risk factor” [34,35]. Data related to dietary exposure of humans to mycotoxins are limited; however there are some published articles in this regard [36-45].

Thousands of dietary components are consumed each day, meaning that a typical diet may provide more than 25,000 bioactive food constituents, and the amounts of bioactive components within a particular food may widely vary [46,47]. Each bioactive food constituent has the potential to modify multiple aspects of the cancer process, either alone or in combination with several micronutrients as well as quantity, timing and duration of exposure modulate the cell response [47].

Lifestyle recommendations for cancer prevention were drawn up on the basis of nutrition-related factors judged to be convincingly or probably causally related to cancer, according to predefined criteria for judging the strength of the evidence regarding causality [47,48]. Concluding, based on the recommendations presented in (Table 1), a healthy diet for cancer prevention is: a diet that allows a person to be as lean as possible without being underweight; a diet rich in fruits, vegetables, whole grains and pulses; a diet that contains low amounts of red meat; a diet that does not contain processed meats; a diet that limits salt intake. Avoidance of sugary drinks, limited intake of calorie-rich foods and limited consumption of alcohol drinks is also recommended for a healthy diet.

Table 1: Lifestyle recommendations for cancer prevention [47].

The links between diet and cancer are complex. The risk of cancer is depending on degree of exposure to contaminated food, availability of nutrients (ex. nutraceuticals) to the body, dietary pattern and lifestyle and food behavior. There are a lot of evidences about specific contaminants known as cancer factor risks but a specific diet with an effective protective role is still unknown.