**1. Introduction**

Excessive body weight is a growing health problem worldwide. It is a well-known risk factor in cardiovascular disease, diabetes, hypertension, and cancers, among other conditions [1]. According to World Health Organization, obesity has been considered as one of the leading threats to future public health.

Obesity is a complex health issue resulting from a combination of causes and individual factors such as behavior and genetics [2]. Behaviors can include physical activity, inactivity, dietary patterns, medication use, and other exposures. Although there are genetic, behavioral, metabolic and hormonal influences on body weight, obesity occurs when you take in more calories than you burn through exercise and normal daily activities that is when energy intake exceeds energy expenditure. Even though the cause of obesity is complicated, dietary habit or lifestyle plays an important role in developing obese conditions [3].

The increasing westernization, urbanization and mechanization occurring in most countries around the world is associated with changes in the diet towards one of high fat, high energy-dense foods and a sedentary lifestyle [4]. Nutrition transition in developing countries leads to dietary intakes of micronutrient – poor, energy – dense foods, which may be important determinants of overweight/obesity [5].

There is also a direct relationship between the amount of dietary fat and the degree of obesity. High-fat diets induce greater food intake and weight gain than highcarbohydrate diets as indicated by animal studies [6]. Contributing factors are caloric density, satiety properties and post-absorptive processing. The satiating effects after meals with a high fat:carbohydrate ratio is less than for meals with a lower ratio.

Mediterranean pattern of nutrition, has been described as containing high proportion of mono-unsaturated fat acids versus saturated fats and contributes in the preservation of body weight, while expands longevity and life expectancy. This pattern of nutrition has been adopted by many countries and it is diversified according to the cultural and socio-economic features of each country. Several research studies have commented on the beneficial effects of the Mediterranean diet in the preservation or decrease of body weight, in the primary or secondary prevention of coronary disease, in the maintenance of high density cholesterol (HDL) and triglycerides within normal rates, as well as in the significant reduction in mortality rates [7–9].

Current recommendations for weight management emphasize the importance of healthy eating patterns that include a variety of nutrient-dense foods, limit portions of energy-dense foods, and reduce overall energy density [10].

A unifying factor for weight loss across dietary patterns is energy density [11]. When a diet's energy density is reduced; it allows individuals to consume satisfying amounts of food for fewer calories. The goal of dietary therapy in the management of obesity is to reduce the total number of calories consumed.

## **2. Physiological causes and effects of obesity**

Obesity is a complex disease that involves an excessive amount of body fat. It is a medical problem that increases your risk of other diseases and health problems, such as heart disease, diabetes, high blood pressure and certain cancers. Although there are genetic, behavioral, metabolic and hormonal influences on body weight, obesity occurs when you take in more calories than you burn through exercise and normal daily activities that is when energy intake exceeds energy expenditure.

Even though the cause of obesity is complicated, dietary habit or lifestyle plays an important role in developing obese conditions [3, 12]. Lifestyle changes and nutritional habits, such as irregular meal patterns; mainly skipping breakfast, consumption of foods and beverages of low nutritional value and sub-optimal intake of dairy products, fruits and vegetables, intake of refined carbohydrates such as sugar sweetened soft drinks are all contributing factors to the development of obesity [12–15].

Obesity as a complex disorder has multiple etiological factors. The primary factor which is considered as a driver of obesity is obesogenic environment and unhealthy eating behavior. Secondary factors such as genetic and neuroendocrine factors, and diseases such as hypothyroidism and polycystic ovary syndrome are also related to excessive weight [16].

In a study carried out among undergraduates in Nigeria observed a significant relationship between vegetable consumption and Body Mass Index (X<sup>2</sup> = 16.031, p-value = 0.001) and there exist no significant relationship between cereals consumption and body mass index (X<sup>2</sup> = 8.916, p-value = 0.710) [17].

Obesity has been shown to be a predisposing factor in the rising prevalence of morbidity and mortality associated with non – communicable diseases like type-2 diabetes mellitus, hypertension, cancer, stroke among adults [18].

Overweight and obesity increases the likelihood of various diseases, particularly heart diseases, type2 diabetes, breathing difficulties during sleep, certain types of cancer and osteoarthritis [19].

#### **3. Dietary fat and obesity**

Fat are of various types, some are more beneficial to health than others. Those found in foods are known as dietary fats, the body needs fat to function fully as it

#### *Diet and Obesity DOI: http://dx.doi.org/10.5772/intechopen.98326*

has a lot of functions in the body and is essential to health. For instance, fat soluble vitamins (Vitamins A, D, E and K) cannot be transported in the absence of fat. However, a diet with too much fat can increase body weight and also increase the risk of cardiovascular disease.

Dietary fats are believed to play an important role in the development of heart disease [20]. The National health institutions has recommended to reduce the intake of dietary fat to prevent CVDs [21].

#### **3.1 Healthy versus unhealthy fat**

The healthy fat are primarily unsaturated fats:

**Monounsaturated fat**: This type of fat is found in a variety of foods and oils. Eating foods rich in monounsaturated fats improves blood cholesterol levels, which in turn decrease the risk of heart disease and may also help decrease the risk of type 2 diabetes.

**Polyunsaturated Fat:** This fat is found mostly in plant-based foods and oils. Omega-3 fatty acids, which is a polyunsaturated fat has been attributed to low rate of heart disease [22]. Also, it helps to raise HDL cholesterol level [23].

Oils such as canola oil, olive oil, corn oil, sunflower oil and peanut oil are made up of monounsaturated and polyunsaturated fats and are liquid at room temperature. Fish such as tuna, salmon, trout, mackerel, herring and sardines are high in omega-3 fatty acids. Plant sources of omega-3 fatty acids are soybean oil, flaxseed oil, and nuts (walnuts, butternuts).

#### **3.2 Unhealthy fats**

Saturated fats and trans fat are often termed unhealthy fats, this is due to the fact that both raise LDL cholesterol levels. High level of LDL cholesterol in the blood increases the risk of heart disease and stroke. A larger amount of saturated fats is from animal sources, including meat and dairy products. Foods high in saturated fat include fatty beef, pork, butter, lard and cream, poultry with skin. Plant-based oils, such as coconut oil, palm oil also contain saturated fats, but do not contain cholesterol.

Trans fat is a product of a process that adds hydrogen to liquid vegetable oils to make them more solid and also refer to as partially hydrogenated oils. These partially hydrogenated oils increase LDL cholesterol and lowers HDL cholesterol which in turn increase the risk of cardiovascular disease. Foods high in trans fat include fried foods, such as French fries, stick margarines and shortenings, pastries, packaged foods, baked goods and pizza dough.

Fatty foods are energy dense and give 9calories per gram compared to carbohydrate and protein that gives 4calories per gram. Also, if physical activity is inadequate, excess consumption of fat can results into weight gain. Also, it does not take as much energy (about 3%), to convert and store dietary fat as it does to convert and store glucose or protein. Fats are quickly and easily stored by the body.

Obesity is a multifactorial and complex affectation that is characterized by a longterm excess energy intake(EI) above energy expenditure (EE) and epidemiological evidence have suggested that a high-fat diet promotes the development of obesity [24].

There is also a direct relationship between the amount of dietary fat and the degree of obesity. An overview of animal studies had indicated that high-fat diets induce greater food intake and weight gain than high-carbohydrate diets [25]. Contributing factors are caloric density, satiety properties and post-absorptive processing. The satiating effects after meals with a high fat:carbohydrate ratio is less than for meals with a lower ratio. It has been reported that the most important variable influencing meal size is the nutrient content of the range of foods consumed and not the level of hunger. Thus dietary fat has a weak effect on satiety and periodic exposure to a high-fat meal, particularly when hunger is high, is sufficient enough to lead to overconsumption of energy as fat in obese patients.

#### **3.3 Influence of dietary fat on weight gain**

An important determinant of body fat is the percentage of dietary energy from fat. Several mechanisms have been proposed to explain why high fat intake might lead to greater body fat [26]. Dietary fat is the most energy dense macronutrient in the diet, providing 9 kcal/g as opposed to 4 kcal/g for carbohydrate or protein; this could lead to overconsumption of energy if food volume is regulated. Fat adds greater flavor and palatability to foods, which could thus increase their consumption.

Fat has a lower thermogenic effect than carbohydrate and protein and this inhibit energy expenditure. A positive energy balance can be the result of overconsumption of energy, perhaps because a high-fat diet has a lower satiating effect per joule than a low-fat diet. A series of studies has produced robust evidence that the fattening effect of dietary fat is linked mainly to the higher energy density of fatty foods compared with carbohydrate and protein rich foods.

In addition, when studied under careful metabolic conditions for short periods, carbohydrate produces a greater thermogenic effect than fat, suggesting that dietary fat may be utilized more efficiently and accumulate as body fat [27]. Carbohydrate intake, but not fat intake, is regulated; thus, individuals on a high-fat diet would tend to consume more total energy to gain the required amount of carbohydrate than would someone on a low-fat diet [28]. Although these mechanisms may seem compelling at face value, foods are not eaten in isolation, and the energy for weight of foods is more determined by the water and fiber content.

Different types of fat contain the same amount of energy, although there are differences in their respective influence on energy balance, energy expenditure and satiety. Low-fat diets and in weight-maintenance diets, have been shown to be affected by the quality of dietary fat. Animal studies have shown that rats fed a diet rich in safflower oil polyunsaturated fats accumulate less body fat than rats fed a diet rich in beef tallow which is a saturated fat [29].

Monounsaturated was found to induce a lower level of postingestive satiety and a larger subsequent energy intake than polyunsaturated and saturated fat in a study on the effect in lean subjects of high-fat meals, differing in fatty acid composition [30].

#### **4. Dietary patterns and obesity**

Dietary patterns that have inverse relationship with obesity include vegan diet, Mediterranean diet and prudent diet. Western diet is directly associated with obesity.

#### **4.1 The vegan diet**

This is a form of vegetarian diet that eliminates meat and animal product, this diet is beneficial to health because it reduces the intake of cholesterol and saturated fat that is predominant in animal product. It has been proven that those who practice a vegan diet minimize their overall risk of coronary heart disease, obesity and high blood pressure.

#### **4.2 The Mediterranean diet**

This diet recommends the use of plant based oil as alternative to butter, it emphasizes adding vegetables to each meal. Avoidance of meat is recommended, though not eliminated. This diet has been proven to help with depression, in addition to controlling blood sugar levels and helping with weight loss. Whole grains, nuts and herbs are also used in larger amounts.
