**5. Effect of food restriction on plaque development is controversial**

In contrast with a normal unrestricted diet, severe food restriction does not promote beneficial effects such as increased collagen synthesis and decreased VCAM-1 expression. On the contrary, plaques of rabbits undergoing food restriction reveal an increase in apoptosis (**Figure 3**). Depending on the cell type and stage of the plaque, apoptosis could be detrimental for plaque stability [29]. Moreover, apoptosis can stimulate the release of inflammatory cytokines and chemotactic factors, thereby further aggravating plaque inflammation [30].

Given that food restriction stimulates autophagy, a well-known cellular survival mechanism, increased apoptosis may seem surprising. However, autophagy induction after intensive nutrient deprivation may be insufficient to counteract apoptosis.

The abovementioned findings are in agreement with previous studies in rabbits showing increased plaque development after a 50% reduction in food intake [31], even though Lacombe et al. [16] reported that aggravated atherosclerosis only occurs in rabbits when dietary restriction is combined with cholesterol feeding. Prenatal under nutrition is also known to program a pro-atherosclerotic phenotype and to accelerate plaque development in young adult offspring [32, 33]. Nonetheless, a large body of evidence indicates that food restriction is associated with a range of positive effects on cardiovascular health. Dietary restriction in apolipoprotein E-deficient mice, for example, results in the development of smaller and less advanced atherosclerotic lesions [7, 34]. A lower incidence of atherosclerotic plaque development is also seen in genetically obese rats consuming a low calorie diet, as compared to rats fed ad libitum [35]. Studies in humans clearly describe a reduction in cardiovascular risk factors but often fail to demonstrate a direct effect on atherosclerotic plaque development [4, 5]. Still, the incidence of atherosclerosis was decreased during the years following World War I and World War II, which supports the general benefit of food deprivation [36]. Importantly, at least two main differences in the experimental design or setup of different studies should be mentioned that may explain a different outcome. First, differences might be related to the severity of food restriction (50% food restriction = moderate, 80% food restriction = severe). Accordingly, severe food restriction holds a higher risk of vitamin deficiency that should be taken into account. Indeed, vitamin D deficiency may contribute to atherosclerosis [37], and also vitamin C and vitamin E depletions are demonstrated to aggravate plaque development [38]. Second, the time span of dietary restriction could be an important factor. Four weeks of food restriction is relatively short in comparison with other studies showing beneficial effects of food restriction. Fontana et al. [4], for example, reported a reduced risk for atherosclerosis in individuals who had been

Food Restriction and Atherosclerotic Plaque Stabilization

http://dx.doi.org/10.5772/intechopen.76560

67

In conclusion, severe short-term food restriction seems to counteract the plaque stabilizing

The authors acknowledge Rita Van den Bossche, Hermine Fret, and Anne-Elise Van Hoydonck for excellent technical support. This study was funded by the University of Antwerp (BOF) and the Flanders Fund for Scientific Research (FWO) (project G.0412.16N). Dorien G. De

Munck is a fellow of the Agency for Innovation by Science and Technology (IWT).

Laboratory of Physiopharmacology, University of Antwerp, Antwerp, Belgium

Dorien G. De Munck, Guido R.Y. De Meyer and Wim Martinet\* \*Address all correspondence to: wim.martinet@uantwerpen.be

on food restriction for an average of 6 years.

benefits of cholesterol withdrawal in rabbits.

**Acknowledgements**

**Author details**

**Figure 3.** Atherosclerotic plaque composition of rabbits that were fed 0.3% cholesterol for 20 weeks (baseline), followed by cholesterol withdrawal for 4 weeks either via a normal diet or a restricted diet (20% of normal diet). (A) Sections of the proximal ascending aorta were TUNEL stained for the detection of apoptosis and the number of TUNEL positive cells in each group was quantified. Scale bar = 50 µm. \*P < 0.05 (One-way ANOVA with post-hoc LSD, n = 10 in each group). (B) Sections of the proximal ascending aorta were immunohistochemically stained for VCAM-1 expression on endothelial cells. The number of VCAM-1 positive endothelial cells in each group was quantified. Scale bar = 500 µm. \*\*P < 0.01 (One-way ANOVA with post-hoc LSD, n = 8–10 in each group).

The abovementioned findings are in agreement with previous studies in rabbits showing increased plaque development after a 50% reduction in food intake [31], even though Lacombe et al. [16] reported that aggravated atherosclerosis only occurs in rabbits when dietary restriction is combined with cholesterol feeding. Prenatal under nutrition is also known to program a pro-atherosclerotic phenotype and to accelerate plaque development in young adult offspring [32, 33]. Nonetheless, a large body of evidence indicates that food restriction is associated with a range of positive effects on cardiovascular health. Dietary restriction in apolipoprotein E-deficient mice, for example, results in the development of smaller and less advanced atherosclerotic lesions [7, 34]. A lower incidence of atherosclerotic plaque development is also seen in genetically obese rats consuming a low calorie diet, as compared to rats fed ad libitum [35]. Studies in humans clearly describe a reduction in cardiovascular risk factors but often fail to demonstrate a direct effect on atherosclerotic plaque development [4, 5]. Still, the incidence of atherosclerosis was decreased during the years following World War I and World War II, which supports the general benefit of food deprivation [36]. Importantly, at least two main differences in the experimental design or setup of different studies should be mentioned that may explain a different outcome. First, differences might be related to the severity of food restriction (50% food restriction = moderate, 80% food restriction = severe). Accordingly, severe food restriction holds a higher risk of vitamin deficiency that should be taken into account. Indeed, vitamin D deficiency may contribute to atherosclerosis [37], and also vitamin C and vitamin E depletions are demonstrated to aggravate plaque development [38]. Second, the time span of dietary restriction could be an important factor. Four weeks of food restriction is relatively short in comparison with other studies showing beneficial effects of food restriction. Fontana et al. [4], for example, reported a reduced risk for atherosclerosis in individuals who had been on food restriction for an average of 6 years.

In conclusion, severe short-term food restriction seems to counteract the plaque stabilizing benefits of cholesterol withdrawal in rabbits.
