The Effect of Short-Term High-Caloric Feeding and Fasting on Bone Microarchitecture

Abstract

Background:

States of chronic overnutrition and undernutrition are both associated with impaired bone health and increased fracture risk but there are no data on bone microarchitecture following short-term controlled nutritional challenges.

Objective:

The purpose of our study was to evaluate the impact of short-term high-caloric feeding and fasting on bone microarchitecture. We hypothesized that both high-caloric feeding and fasting would have negative effects on microarchitecture.

Materials and Methods:

We recruited 23 adult healthy subjects (13 males, 10 females, mean age 33.2±1.4 years, mean BMI 26.0±1.5 kg/m²). Subjects underwent an in-patient 10-day high-caloric visit (caloric intake with goal to achieve 7% weight gain), after which they went home to to resume a normal diet for 13-18 days (stabilization period), and were then readmitted for a 10-day in-patient fasting stay (no caloric intake). All subjects underwent HRpQCT (XtremeCT, Scanco Medical AG, Brüttisellen, Switzerland) of the distal tibia and distal radius after each visit to assess volumetric bone mineral density (vBMD), trabecular and cortical microarchitecture, and strength estimates. The Wilcoxon signed rank test was used to perform within group comparisons.

Results:

During the high-caloric period, there was a mean increase in weight by 6.3+1.7% (p<0.0001). There were no significant changes in bone parameters in the distal tibia or distal radius (p>0.05). During the stabilization period there was a significant reduction in weight by −2.7+1.9% (p<0.0001) but no change in bone parameters (p>0.05). During the fasting period there was a further reduction in weight by −8.8+1.2% (p<0.0001). In the distal tibia, there was a significant increase in total and cortical vBMD, trabecular and cortical parameters as well as strength estimates (p<0.05). In the distal radius there was an increase in total and trabecular vBMD (p<0.05), while there were no changes in other microarchitecture parameters or strengths estimates.

Conclusion:

Short-term fasting after high-caloric feeding improves vBMD, bone microarchitecture and strength estimates of the distal tibia, while short-term high-caloric feeding does not change vBMD or microarchitecture. These results suggest that short-term fasting after high-caloric feeding in healthy individuals improves bone health and that these changes can be detected using HRpQCT in-vivo.

1. Introduction

States of chronic overnutrition and undernutrition are both associated with impaired bone health and increased fracture risk [1-5]. While bone mineral density (BMD) is generally normal or even high in individuals with obesity [1, 6], impaired bone quality and bone microarchitecture are determinants of increased fracture risk in this population [7, 8]. A short-term high-fat diet in mice has been shown to reduce cortical and trabecular microarchitecture in young developing mice, but only impaired cortical microarchitecture in mature mice [9], while in another study a high-fat diet showed initial increase in trabecular bone mass which decreased after long-term feeding [10]. Bone loss and increased fracture risk are well-known complications of anorexia nervosa, a state of chronic undernutrition [11]. Women with anorexia nervosa have low BMD, impaired bone microarchitecture and lower bone strength estimates [12, 13]. Long-term 25% caloric restriction in normal-weight individuals has been shown to reduce BMD [14]. In contrast, lifelong 40% caloric restriction in mice has been shown to delay age-related trabecular bone loss [15], while short-term caloric restriction in adult mice did not lead to significant changes in bone microarchitecture [15]. Of note, short-term diets in these studies were 4 to 8 weeks in length.

Bone microarchitecture and strength estimates of the distal tibia and distal radius can be assessed non-invasively in humans using high-resolution peripheral quantitative computed tomography (HRpQCT) which allows longitudinal assessment after dietary interventions. The purpose of our study was to evaluate the impact of short-term high-caloric feeding and fasting on bone microarchitecture. We hypothesized that both high-caloric feeding and fasting would have negative effects on microarchitecture.

2. Materials and Methods

This study was Institutional Review Board-approved, and written informed consent was obtained from all subjects.

2.1. Subjects and Study Design

The study subjects and the protocol have been described previously [16, 17]. In brief, subjects were recruited from the community through advertisements. Inclusion criteria were ages 18 to 45 years, normal weight or overweight, and eumenorrhea in women. Exclusion criteria were chronic illnesses and use of medication that could influence bone metabolism, estrogen use within the last three months, and a history of an eating disorder. Study subjects were admitted to our clinical translational research center for 10 days for the high-caloric visit (day 1 to day 10). The goal of the visit was to achieve 7% weight gain (macronutrient content of the diet: 45-55% carbohydrates, 30-40% fat, and <25% protein). After the high-caloric visit, subjects went home for 13-18 days and resumed a normal diet (stabilization period, day 10-25). Subsequently, subjects were readmitted for a 10-day fasting stay (no caloric intake, water ad libitum, daily multivitamin containing 400 IU of cholecalciferol and 60mg of calcium, 20 mEq of potassium chloride and 200mg of allopurinol daily to prevent hypokalemia and hyperuricemia, day 25 - 35). A food frequency questionnaire capturing calcium and vitamin D intake over the prior month and a Nutrition Data System for Research (NDSR) food record capturing vitamin D intake over the prior four days, were administered prior to the high caloric visit and prior to the fasting visit. Clinical characteristics of the cohort have been reported previously [16, 17], however, no data on bone microarchitecture have been reported.

2.2. High-resolution peripheral quantitative computed tomography (HRpQCT)

All subjects underwent HRpQCT (XtremeCT, Scanco Medical AG, Brüttisellen, Switzerland) of the distal tibia and distal radius to assess volumetric BMD (vBMD) and trabecular and cortical microarchitecture. The non-dominant extremity was scanned unless there was a history of fracture, in which case the non-fractured side was assessed. Scans were performed at baseline, after the high-caloric stay, after the stabilization period, and after the fasting period. A fixed region of interested of 22.5 mm and 9.5 mm from the distal tibial and radial articular surface, respectively, was used, and 110 CT slices were obtained with an isotropic voxel size of 82 μm³, delivering a three-dimensional representation of approximately 9 mm in the axial direction. The volume of interest was then automatically separated into a cortical and trabecular region using a threshold-based algorithm. Automated analysis provided information regarding total, trabecular and cortical vBMD. Standard trabecular and cortical microarchitecture parameters (trabecular thickness, trabecular number, cortical thickness) and individual trabecular segmentation (trabecular plate volume fraction and trabecular plate thickness) [18-20] as well as extended cortical analysis (cortical pore volume) [21] were obtained. Microfinite element analysis (FEA) was performed to assess estimated failure load in the setting of axial compression [22]. Two-dimensional image registration was performed for baseline and follow-up scans [23], with at least 80% overlap for all scans for a given participant.

2.3. Statistical Analysis

We used JMP Statistical Discovery Software (Version 12, SAS Institute, Carey, NC) for statistical analyses. Changes within groups during the high-caloric visit, the stabilization period, and the fasting visit, were assessed using the Wilcoxon signed rank test. P ≤ 0.05 was used to denote significance. Data are presented as mean ± standard error of mean (SEM).

3. Results

3.1. Clinical Characteristics

We recruited 23 adult healthy subjects (13 males, 10 females, mean age 33.2±1.4 years, range 22-44 years) who were of normal weight or overweight (mean BMI 26.0±1.5 kg/m², range 23.3-27.9 kg/m²) (Supplement 1). None of the subjects had a history of an eating disorder or metabolic disease, such as diabetes mellitus. Three subjects were taking multivitamins prior to the study. Total mean daily calcium and vitamin D intake assessed by a FFQ before the high-caloric visit was 1113±175 mg and 323± IU, respectively. Total mean daily calcium and vitamin D intake before the fasting visit 1237±136 mg and 364±52 IU, respectively (Supplement 2).

3.2. Bone microarchitecture during the high caloric period

During the high caloric period, there was a mean increase in weight by 6.3±1.7% (p<0.0001). There were no significant changes in bone microarchitecture parameters or strength estimates of the distal tibia or distal radius (Table 1 and 2, Figure 1).

Table 1:

Percent change in bone microarchitecture and strength estimates of the distal tibia during the high-caloric visit, the stabilization period, and the fasting visit. Data are expressed as means and standard error of the mean.

	High-calorie visit	Stabilization period	Fasting visit
Volumetric Bone Mineral Density (vBMD)
% change in total vBMD	−0.08 ± 0.10	−0.11 ± 0.13	0.30 ± 0.11***
% change in trabecular vBMD	−0.34 ± 0.18	0.12 ± 0.19	0.18 ± 0.19
% change in cortical vBMD	−0.19 ± 0.22	−0.23 ± 0.18	0.53 ± 0.16***
Trabecular Microarchitecture
% change in trabecular thickness	−0.89 ± 1.45	0.04 ± 1.61	4.60 ± 1.51 *** ^^
% change in trabecular number	0.96 ± 1.54	0.77 ± 1.69	−3.90 ±1.61*** ^
% change in trabecular plate volume fraction	−1.57 ± 1.25	−0.44 ± 1.57	3.47 ±1.34***
% change in trabecular plate thickness	−0.15 ± 0.31	−0.04 ± 0.16	0.51 ± 0.21**
Cortical Microarchitecture
% change in cortical thickness	0.78 ± 0.81	0.54 ± 0.57	0.06 ± 0.37^^
% change in cortical pore volume	6.25 ± 3.35	3.37 ± 3.08	−0.39 ±1.83***
Strength estimates
% change in failure load	−0.44 ± 0.27	0.22 ± 0.50	0.55 ± 0.40**

^*p<0.05

^**p<0.02

^***p<0.009

^{^^}p<0.05 increase compared to pre-intervention baseline of the study

^{^}p<0.05 decrease compared to pre-intervention baseline of the study

Table 2:

Percent change in bone microarchitecture and strength estimates of the distal radius during the high-caloric visit, the stabilization period, and the fasting visit. Data are expressed as means and standard error of the mean.

	High-calorie visit	Stabilization period	Fasting visit
Volumetric Bone Mineral Density (vBMD)
% change in total vBMD	−0.35 ± 0.29	−0.11 + 0.13	0.50 + 0.26*
% change in trabecular vBMD	−0.25 + 0.377	−0.22 + 0.31	0.75 + 0.27***
% change in cortical vBMD	−0.07 + 0.18	−0.26 + 0.24	−0.07 + 0.17
Trabecular Microarchitecture
% change in trabecular thickness	−0.63 + 2.14	0.09 + 2.23	1.85 + 2.34
% change in trabecular number	1.48 + 2.39	0.69 + 2.46	−0.14+2.12
% change in trabecular plate volume fraction	−3.09 + 2.64	0.37 + 2.19	3.01 + 2.68
% change in trabecular plate thickness	0.24 ± 0.30	−0.42 ± 0.29	0.50 ± 0.28
Cortical Microarchitecture
% change in cortical thickness	0.19 + 0.32	−0.97 + 1.05	−0.22 + 0.37
% change in cortical pore volume	−2.68 + 4.89	7.51 + 8.83	5.79 +3.88
Strength estimates
% change in failure load	−0.69 ± 0.98	−0.08 + 1.02	0.27 + 0.59

^*p<0.05

^**p<0.02

^***p<0.009

Figure 1:

Change in volumetric bone mineral density, trabecular microarchitecture, and strength estimates of the distal tibia after the high-calorie visit, the stabilization period, and the fasting visit. There was a significant change of bone parameters during the fasting visit. Data are reported as mean ± SEM. *p<0.02.

3.3. Bone microarchitecture during the stabilization period

During the stabilization period there was a significant reduction in weight by −2.7±1.9% (p<0.0001). There were no changes in vBMD, microarchitecture or strength estimates of the distal tibia or distal radius (Table 1 and 2, Figure 1).

3.4. Bone microarchitecture during the fasting period

During the fasting period, there was a further reduction in weight by −8.8±1.2% (p<0.0001). In the distal tibia, there was a significant increase in total and cortical vBMD (p<0.009). There was also an increase in trabecular thickness and decrease in trabecular number, and an increase in trabecular plate volume fraction and plate thickness (p<0.05). There was a reduction in cortical pore volume (p<0.05). Failure load (a strength estimate) increased (p<0.02) (Table 1 and Figure 1).

In the distal radius there was an increase in total and trabecular vBMD (p<0.05), while there were no changes in other microarchitecture parameters or strengths estimates (Table 2).

When compared to the baseline visit of the entire study (pre-intervention baseline visit), there was a significant increase in trabecular thickness, reduction in trabecular number, and increase in cortical thickness in the distal tibia following the fasting visit (p<0.05) (Table 1). In the distal radius, there were no significant differences in bone parameters following the fasting visit compared to the pre-intervention baseline visit.

4. Discussion

Our study showed that short-term fasting in healthy individuals improved vBMD, trabecular and cortical bone microarchitecture and strength estimates of the distal tibia, and increased vBMD of the distal radius, while there were no significant changes of the remaining parameters in the distal radius. Short-term high caloric intake did not lead to a significant change of vBMD, bone microarchitecture parameters or strength estimates of the distal tibia or radius.

It is well-known that women with anorexia nervosa, a state of chronic undernutrition, have low BMD, impaired bone microarchitecture, lower bone strength estimates, and increased fracture risk [12, 13]. However, the effect of caloric restriction on bone in healthy normal-weight individuals is debated. A 2-year randomized clinical trial of 25% caloric restriction in nonobese young adults showed bone loss of the lumbar spine and hip [14]. Bone loss was also found to occur after weight loss in the elderly, especially postmenopausal women [24-26]. However, a 6-month weight loss intervention in overweight/obese men improved tibial cortical thickness compared to a control group [27]. Murine studies have shown that caloric restriction delayed age-associated trabecular bone loss [15, 28]. Moreover, caloric restriction increased vertebral BMD of the SENCAR mouse model and of obese C57BL/6 diabetes-prone mice [29]. However, no study has examined the effects of short-term fasting on bone microarchitecture and strength estimates in healthy normal to overweight individuals.

We detected a significant increase in trabecular and cortical bone parameters of the distal tibia after 10 days of fasting. Of note, study participants received a daily multivitamin containing 400 IU of cholecalciferol. In addition, the fasting visit followed the high caloric visit and the stabilization period and the improvement in bone variables might reflect improvement from the detrimental effects of the high-caloric intervention; however, we did not detect a deleterious effect of a short-term high calorie diet on bone microarchitecture. When compared to the baseline visit of the entire study (pre-study baseline), there was a significant increase in trabecular thickness, reduction in trabecular number, and increase in cortical thickness in the distal tibia following the fasting period. However, no significant change in the other microarchitecture parameters that increased during the fasting period was detected when compared to the pre-study visit, suggesting that the observed improvements in microarchitecture might reflect a response to the detrimental changes from high-caloric feeding. The reason why improved bone microarchitecture and strength estimates involved only the distal tibia (weightbearing bone) and not the radius (non-weightbearing bone), is unclear.

While obesity was thought to be beneficial for bone health because of increased mechanical loading, recent studies have highlighted adverse effects of obesity on skeletal integrity. Increased fracture risk, especially extremity fractures, have been demonstrated in patients with obesity [1-3]. Animal studies have shown increased bone resorption and reduced formation following diet-induced obesity [30, 31]. Obesity is also associated with chronic inflammation and proinflammatory cytokines and lipoproteins, which have been identified as potential mechanisms of increased bone resorption and decreased bone formation, leading to low BMD, impaired microarchitecture and lower strength estimates [30-32]. We did not observe a statistically significant change in bone parameters following the high-caloric diet, however, our observed improvement in bone microarchitecture and strength estimates after fasting might represent a response to the detrimental effects of high-caloric feeding on bone.

We have recently shown increased BMAT in the axial skeletal following short-term high-caloric feeding and fasting with reciprocal changes in the peripheral skeleton [16, 17]. BMAT was long considered an inert filler of bone marrow space in response to bone loss, however, marrow adipogenesis and bone formation can coexist, and high BMAT has been found in states of bone formation, such as puberty, or high BMD, such as in type 2 diabetes [33]. Our findings of an increase in BMAT and an increase in trabecular and cortical bone during fasting supports the notion that BMAT may serve as an energy depot in certain situations and can increase with bone formation.

Limitations of our study include the relatively small study population. However, with 23 subject we were able to detect significant changes in bone microarchitecture and strength estimates. In addition, the order of the high caloric visit and fasting visit were fixed in all subjects, and the observed changes might have differed if the order of the intervention had been reversed. Main strengths of our study were the controlled in-patient caloric interventions and the use of longitudinal HRpQCTs to assess trabecular and cortical microarchitecture and strength estimates following each visit.

In conclusion, short-term fasting after high-caloric feeding improves vBMD, bone microarchitecture and strength estimates of the distal tibia, while short-term high-caloric feeding does not change bone microarchitecture. These results suggest that short-term fasting after high-caloric feeding in healthy individuals improves bone health and that these changes can be detected using HRpQCT in-vivo.

Highlights.

• Chronic overnutrition and undernutrition is associated with impaired bone health

• Short-term fasting improved tibial density and microarchitecture

• Short-term fasting improved tibial strength estimates

• High-caloric diet did not change bone parameters

• HRpQCT can assess bone microarchitecture after short-term nutritional challenges