**3. The nutritional differences of dried fruit**

Nuts are also called lipid fruit, as they are low in water and high in fat. The most common are:


The queen of dried fruit is the walnut. The walnut is a very ancient plant; 9000 years ago, people started talking about this fruit. The name derives from the Latin "nux nucis," which included the walnut and similar fruits, those with a fleshy kernel, wooden shell, and fibrous rind.

The *Jungals regia* fruit tree (or white walnut) produces a fruit, the drupe, which is fleshy and composed of the husk (the fibrous outer part), and the shell (endocarp) that is the woody inner part. Inside the shell is the seed (kernel), which is edible. This plant, to date, is cultivated in many parts of the world with different cultivars:


Chandler is the most cultivated and resistant to infections and diseases among all these cultivars.

The nutritional characteristics per 100 g of walnuts are as follows:


*This is the Nut You Should Be Eating for Better Gut Health DOI: http://dx.doi.org/10.5772/intechopen.108567*


#### **4. Benefits of dried fruit**

Nuts are a valuable ally of our heart; their composition, especially of unsaturated fatty acids, helps reduce inflammation, improves blood pressure control, and regulates blood cholesterol levels: phytosterols, fiber, and mono- and polyunsaturated fatty acids help to contain LDL (the cholesterol dangerous for the heart) and to maintain reasonable levels of HDL (the "good" one), reducing the process of atherosclerosis and thus limiting the risk of blockage of the arteries.

In literature, there are many scientific studies with walnut as the protagonist. It is present in many dietary regimes, mainly the Mediterranean diet.

Among its nutritional characteristics, walnut is rich in good fats, especially omega-3 fatty acids, such as alpha-linolenic acid (ALA). The latter is the primary omega-3; it is an "essential" polyunsaturated fatty acid because our body cannot produce it on its own, hence the importance of consuming it with the diet. ALA keeps blood cholesterol levels low.

Walnut is also a source of essential minerals such as iron, magnesium, phosphorus, potassium, zinc, copper, and vitamin E—a powerful antioxidant. It does not contain cholesterol but a minimum amount of saturated fats and an overall percentage of mono- and polyunsaturated fats. This feature allows it to provide energy and carry vitamins (folate, niacin, and vitamin E) and minerals (magnesium and potassium), which are helpful not only for bone health, muscles, heart, and circulation, but also for the brightness of the skin and the strength of the hair.

Mono- and polyunsaturated fats are the components of cell membranes and some hormones, and they help keep the immune system active and the blood thin. They also contain bioactive compounds and protective substances such as tocopherols, phytosterols, and phenolic compounds and proteins and carbohydrates in balanced quantities and lots of fiber.

Given its composition, the walnut turns out to be a high-calorie food, so its consumption must be carefully dosed. An average walnut weighs about 8 g with a caloric intake of 35 kcal. Nutrition specialists recommend an intake of 15 g of walnuts per day for a caloric consumption of approximately 100 kcal.

Walnuts are very versatile in diets; they can be eaten as a snack or as a dessert, but they can also be associated with other foods, making them more palatable.

Given its nutritional characteristics, walnut is not considered only as a fruit or food. The European Commission, in regulation 43/2012, defined walnut as a natural nutraceutical food [16] as it improves the elasticity of blood vessels if consumed with a dose of 30 g per day. The nutraceutical power is given by the number of plant sterols, notably polyphenols, whose biological activity is potent. There are also large quantities of ellagitannins and ellagic acid, with antiviral, antibacterial, and antitumor properties [17].

Comparison with observational studies on European and American populations has shown that the Mediterranean diet, where walnuts are very present, leads to a reduced risk of mortality from numerous diseases over a 10-year follow-up [18].

A report on the PREDIMED study revealed that a group of about 1200 patients who followed the Mediterranean diet with walnut supplementation for 1 year gave a 14% reduction in the prevalence of metabolic syndrome, compared to a 2% reduction in the group assigned low-fat diet [19].

Another cross-sectional study compared four different diet regimens in a multi-ethnic group in North America. The group following a diet with cereals, fruit, and nuts showed a reduced risk of cardiovascular disease and a positive effect on inflammatory markers (inflammatory biomarkers, endothelial function, and homocysteine) [20].

From the scientific evidence, it can be asserted that the consumption of walnuts has a lipid-lowering effect; they reduce the risk of developing diabetes, especially in the female population and are not associated with weight gain and therefore not associated with obesity [21].

A recent meta-analysis evaluated the effect of walnut consumption on all causes of mortality from cardiovascular disease to cancer. The cohort studies were analyzed to support the decrease in mortality in individuals who eat walnuts [22].

Walnuts contain various dietary nutrients such as fiber, vitamins (folic acid, niacin, tocopherols, and vitamin B6), minerals (calcium, magnesium, and potassium), phytosterols, and phenolic compounds [23].

The fats present in walnuts are low in SFA and high in MUFA (oleic acid), with an abundant amount of PUFA (a-linolenic acid, omega 3) [24]. We also find a high content of L-arginine, a precursor of nitric oxide, with vasodilating power [25].

The cholesterol-lowering power is given by the phytosterols present in walnuts [26].

A recent study on the Chinese-Asian population targeting the prevention of type II diabetes mellitus and glycemic changes has considered the postprandial glycemic response (0–120 min) after the administration of high-protein nut bars compared to the administration of high-carbohydrate cereal bars. About 16–28 g of mixed nuts were also given daily. The objective was to evaluate the postprandial response of overweight adults with an increased risk of developing type 2 diabetes. The study showed that the intake of walnut bars suppressed the glycemic response and improved the postprandial hyperglycemic response. The high-risk group observed a 30% reduction in the overall glycemic impact [27].

Previous studies have confirmed the association between walnut intake and decreased cardiovascular risk and the development of type 2 diabetes mellitus [28, 29].

Some previous studies have shown that the intake of nuts suppresses postprandial blood sugar caused by the intake of foods rich in carbohydrates [30, 31].

#### **5. Microbiome and dried fruit**

Numerous families of bacteria populate the microbiome present in our intestines [32]. Numerous factors influence microbiota, such as age, diet, drugs, and the environment. These impact bacterial families in metabolizing nutrients derived from our diet and some drugs. The microbiota is a form of barrier for our intestines, it protects us from infections and, at the same time, it produces molecules (proteins, fatty acids, etc.) that participate in numerous physiologicals processes.

When the microbiome is altered, characteristic intestinal disorders such as irritable bowel syndrome (IBS) [33], constipation [34], and abdominal bloating can be correlated [35].

#### *This is the Nut You Should Be Eating for Better Gut Health DOI: http://dx.doi.org/10.5772/intechopen.108567*

The intake of walnuts is healthy not only to reduce cardiovascular risks but also to promote the balance of intestinal bacteria in our microbiota.

Walnuts can be considered prebiotics and probiotics due to their bacterial content. Their peel contains many fibers. Their fermentation promotes the production of SCFA (such as butyrate, which optimizes intestinal contractility and mucus secretion) [36] and polyphenols with the antioxidant and anti-inflammatory properties.

It can be said that the consumption of dried fruit particularly promotes the growth of the Rosuberia bacterial family, which protects the intestinal lining. The bacterial family Eubacteria Eligens also grows after the intake of walnuts and is associated with an improvement in blood pressure.

The bacterial family of Lachnospiraceae has been associated with more significant reductions in blood pressure, total cholesterol, and non-HDL cholesterol.

In 2020, a systematic review and meta-analysis of controlled studies on the effect of nut intake on the microbiota was published. The study also evaluated bowel function and its symptoms in healthy adults [37].

Studies with findings related to fecal microbiota were included in the review; all studies measured how phyla behaved after walnut intake, in particular Actinobacteria, Bacteroidetes, Firmicutes, Proteobacteria, and Verrucomicrobia [38, 39].

From this comparative study, it can be confirmed that the consumption of walnuts affects the composition of the microbiota. Still, given the results, there is a confirmation at the level of gender and not directly on the species or the diversity, depending on the duration of intake of the walnuts. Although the number of comparative studies is few, the study on the effects of nut consumption on the microbiota needs further trials [40].

In another comparative study [41], the microbiota was evaluated in a pediatric and adult population. All enrolled children had reached the age of three, as a 3-year-old child's microbiota is comparable to an adult's [42]. This population was given whole or partially processed walnuts and compared with populations that either did not eat walnuts or ate them in negligible doses.

The studies measured the microbiota with innovative techniques, with complete analyses allowing for quantification and taxonomic identification.

The Holscher study was compared where the population was given 42 g of walnuts daily for three weeks. No significant differences were found in the size of the entire sample, but the intake of walnuts significantly influenced the bacterial families. A decrease in Actinobacteria and a substantial increase in Firmicutes were observed. An increase in the genera Faecalibacterium, Clostridium, Roseburia (cluster of Clostridium XIVa and IV), and Dialister (49–160% more relative abundance) and a reduction in the genera Ruminococcus, Dorea, Oscillospira, and bifidobacteria (16–38% relative abundance inferior) were also observed [39].

From the data that emerged, it can be deduced that a diet with numerous different foods can temporarily reduce microbial diversity. This consequence is called the "shock effect." These results contradict those in the scientific literature, suggesting that adherence to a varied dietary model increases intestinal microbial diversity [43]. In numerous dietary models and, in particular, in the Mediterranean diet, microbial changes are already measured after three to four days of adherence to the diet [44].

From this study, it was concluded that among the various types of dried fruit, nuts are the ones that have the most significant effect on the microbiome due to their abundance of polyphenols and omega 3, considered prebiotics. The limitation of these studies is the numerical scarcity and the data collected in the microbiome after short-term intake of walnuts [41].
