Comparison of Alkaline and Acid Base Diet Profiles and its Correlation with Bone Mineral Density: A Cross Sectional Investigation

Transcription

1 Comparison of Alkaline and Acid Base Diet Profiles and its Correlation with Bone Mineral Density: A Cross Sectional Investigation Item Type Thesis Authors Aguayo, Izayadeth Publisher The University of Arizona. Rights Copyright is held by the author. Digital access to this material is made possible by the College of Medicine - Phoenix, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 14/08/ :06:31 Link to Item

2 Comparison of Alkaline and Acid Base Diet Profiles and its Correlation with Bone Mineral Density: A Cross Sectional Investigation A thesis submitted to The University of Arizona College of Medicine Phoenix in partial fulfillment of the requirements for the degree of Doctor of Medicine Izayadeth Aguayo Class of 2016 Mentor: Carol Johnston, PhD

3 Dedication This project is dedicated to my parents, who have instilled in me the love of caring for one s body through a healthy lifestyle.

4 Acknowledgements This study would not have been possible without the help and direction of my mentor Carol Johnston, Ph.D. Thank you so much for your unwavering support and mentorship. Thank you also to Jessica Knurick, Ph.D. and the team for their support in completing my thesis requirements.

5 Abstract Previous studies suggest that dietary patterns that promote acidosis may have a negative effect on bone density, whereas a more alkaline based profile would be associated with better bone health. Thus, the aim of this study was to assess, in omnivores, vegetarians, and vegans bone mineral density using Dual energy X ray absorptiometry (DEXA) and compare it to their acid base status as indicated by urinary ph, Potential Renal Acid Load (PRAL) and serum anion gap. Our hypothesis was that plant based diets would be associated with a more alkaline acid base profile than omnivorous diets, and thus have a higher bone mineral density. Methods: We conducted a cross sectional study where we compared plant based vs. omnivorous diets. Eighty two subjects were enrolled in the study (27 omnivores, 27 vegetarians, and 28 vegans). Subjects were asked to fill out a medical history form and a 24 hour diet recall, and to complete a 24 hour urine collection. After a few weeks, subjects returned to the test site to complete a DEXA scan. Acid base balance and bone health were determined using PRAL, urine ph, and anion gap as biomarkers for ph, and DEXA as an indicator of bone density. Our results showed that bone mineral density did not differ significantly between groups, although lacto ovo and vegan diets were more alkaline compared to meat based diets ( , , and ph respectively, p = 0.003). Protein intake was found to be reduced by ~30% in individuals adhering to a lacto ovarian or vegan diet; yet protein was only associated with bone mineral density in those following vegan diets. Conversely, urinary ph was associated with bone mineral density only in those following a meat based diet. The significance of this study is that it provides knowledge in the area of osteoporosis prevention and perhaps specific recommendations based on diet groups: increased fruit and vegetable intake for those with high meat consumption, to improve the acid base homeostasis, and increased plant protein intake for individuals who follow a plantbased diet.

6 Table of Contents Introduction... 1 Research Materials and Methods... 2 Results... 6 Discussion References... 16

7 Figures and Tables Table 1: Participant characteristics by diet group Table 2: Bone mineral density and urinary measures by diet group Table 3: Dietary intake for nutrients associated with bone health by diet group Table 4: Correlation coefficients for urinary ph and protein significantly correlated with BMD in at least one diet group

8 Introduction/Significance Osteoporosis is a growing public health concern, with predicted osteoporotic fractures reaching epidemic proportions due to prolonged life expectancies of the elderly. 1 There is a need for dietary and lifestyle measures to address the concern of low bone mineral density in susceptible populations. The lifetime risk of post menopausal women having an osteoporotic related fracture is about 40% 2 and in the elderly, hip fractures are associated with mortality rates of about 20%. 3 Thus, strategies targeting the prevention of poor bone health are urgently needed, with emphasis placed on modifiable factors such as nutrition. 4 However, whether certain lifestyle factors can predict the risk of osteoporosis is inconclusive and controversial. 5 Osteoporosis is a common metabolic disease that is multifactorial and is influenced by lifestyle, age, genetic, and dietary factors. 2 Vegetarian diets and their effect on bone health has been a topic of interest for many years, but what data is available is inconclusive. 4 Yet there is strong evidence that a diet rich in fruits and vegetables is protective against many chronic diseases. 6 Population based studies from 2001 and 2003 have demonstrated benefits from the intake of fruits and vegetables on axial and peripheral bone mass in individuals. 4 In addition, it has been hypothesized that reduced animal protein is beneficial for bones because of the reduced acid load. 5 Several investigators believe that increased acid load is a contributing factor in the development of osteoporosis. 2 For example, distal renal tubular acidosis, an impairment in renal acid excretion by the kidneys leading to acid accumulation in the body, has been show to affect bone histology and bone mineral density. 7 This finding shows the casual relationship of acidosis in the suppression of bone formation and function. 7 The human body tightly regulates acid base homeostasis. If the diet is low in Mg, K, and Ca, which are associated with alkali salts such as citrate or carbonate, bones will release those cations along with alkali salts. 8 Over time this process will lead to reduction in bone mineral content and bone mass. 8 There has been substantial evidence that certain foods affect acidbase balance in the body. In general, a high protein diet is associated with being more acidic, while a fruit and vegetable diet has more of an alkalizing effect, and can reduce the acid load. 6 Since the 1960s its been proposed, first by Wachman and Bernstein, that osteoporosis can develop if the body needs to regulate the acid base balance substantially. 6 There have been 1

9 studies that have shown a positive relationship between high protein diets and hip fractures. 6 Therefore, consuming fruits and vegetables is important to buffer the acid load imposed by high protein diets. 6 Experts suggest that the increased incidence of osteoporosis with age may be related to the lifelong buffering with basic salts from the bone to counteract the imbalance of acid base homeostasis. 4 In essence, bone minerals are buffer bases, and the lifetime accumulation of buffering of the acid load via bone minerals leads to the gradual loss of bone. 3 As described in the study by New, if 2 meq/kg per day of calcium is required to buffer approximately 1 meq/kg per day of acid, over 10 years this would lead to a 15% loss of bone mass, assuming 1 kg of calcium in the body. 4 A drop in ph (acidosis) has also been associated with bursts in bone resorption by activation of mature osteoclasts. 4 Thus, the authors of that study propose that vegetable based diets are beneficial to bone health. 4 To our knowledge, very few studies have been published looking at the correlation between acidosis and bone mineral density. However, whether reduced acid load is beneficial for bones is controversial, since some studies show no difference in fracture rates between vegetarians and non vegetarians. 5 Nonetheless, the treatment of osteoporosis best lies in prevention and it is worthwhile to consider the effect of acid base status. Thus, our aim was to assess the bone health of omnivores, vegetarians, and vegans using DEXA and compare their acid base status by urinary ph, serum anion gap, and PRAL. Our hypothesis was that plant based diets would provide more cations such as potassium and magnesium along with basic salts which neutralize acid, leading to a more alkaline acid base profile and thus higher bone mineral density. 2

10 Research Material and Methods Subjects Approximately ninety males and pre menopausal females, ranging in age from years, volunteered to participate in this study. Subjects must have been following their respective diets for at least 1 year, were not endurance trained, and were not obese (BMI >30 kg/m 2 ) or diagnosed with diabetes Type 1 or 2. Subjects did not have any known chronic diseases, take any prescribed medications (other than oral contraception) or use recreational drugs; females demonstrated a regular menstrual cycle and had no history of pregnancy within the preceding six months. Approval for this study was obtained from the Arizona State University Internal Review Board, and all subjects completed written informed consent form prior to participation. Participants were categorized according to their response to the following four questions: 1 How many times per week do you consume meat, fish, or poultry? 2 How many times per week do you consume diary products (milk, cheese, butter, yogurt)? 3 How many eggs do you consume per week? 4 How long have you been following your current diet? Subjects who consumed at least 3 servings of meat were considered omnivores. Those who consumed between zero and three were excluded from the study. Participants who reported never consuming meat, eggs, or dairy products were considered vegan, and those who reported never eating meat, fish or poultry, but consumed at least three servings of diary and/or three eggs per week were considered lacto ovo vegetarians. All participants reported following their specific diets for at least one year. 3

11 Research Design/Procedures This study utilized a cross sectional design to obtain information from three distinctive groups. Approximately ninety males and premenopausal females were recruited from the greater Phoenix area. An online survey was used and subjects who met the inclusion criteria were asked to report to the research laboratory on two separate occasions. Visit 1 Subjects consented to the study and subsequently filled out a medical history form, which included details on age, gender, smoking status, medical history, and activity level. Participants also completed a 24 hr dietary food recall conducted by a trained nutritionist who also completed the nutritional analysis (Food Processor version 7.71; ESHA Research, Salem, OR). Measurements such as height, body weight, and waist circumference were obtained, including body fat percentage and bone mineral density using the dual energy X ray absorptiometry, also known as the DEXA scan (DXA; Lunar idxa, General Electric Company, East Cleveland, OH, USA). Prior to the DEXA scan women were required to have a negative pregnancy test. Then subjects were instructed to complete a 24 hr urine sample the day before the second visit, which involved obtaining all urine voids for an entire day, specifically discarding the first void of urine in the morning, collecting every void thereafter, including the void of the morning of the second visit. Subjects were provided with urine containers and collection vessels. Visit 2 Subjects returned to the laboratory for a second visit following a 12 h overnight fast. Subjects turned in a 24 h urine sample from the previous day and had their blood drawn by a registered nurse. 4

12 Data Analysis and Statistical Analysis Urinary calcium and the blood anion gap were measured at Sonora Quest Laboratories in Tempe, Arizona. Urinary ph was determined using a ph meter (WTW Chekmite ph 20 Sensor, Nova ph, Woburn, MA, USA). The validated REAPS scoring system was used to assess diet quality between the three groups. Potential renal acid load, PRAL, was estimated from dietary intake using the following equation: (0.49 protein (g)) + (0.037 P (mg)) (0.021 K (mg)) (0.026 Mg (mg)) (0.013 Ca (mg)) [15]. The physical activity level of the participants was approximated using a validated questioner and converted into metabolic equivalents (METS) [13]. All statistical analyses were performed using the Statistical Package for the Social Sciences (SPSS for Windows, version 21.0, SPSS Inc., Chicago, Il). Subject demographic data was evaluated using descriptive statistics, including means and standard deviations. Differences between means were analyzed while controlling for age, BMI, and gender via univariate analyses. The data was normalized and if the transformation did not normalize the data, the Kruskal Wallis test was used. Chi Square analysis was used to compare nominal data and Pearson s correlation was used to identify associations between variables, while controlling for confounding factors such as age, BMI, and gender; p values were considered statistically significant when p

13 Results Over 400 people completed the online survey, with only 82 meeting the study requirements and enrolling in the study. The study had a 100% retention rate. As stated earlier, the individuals were divided into three groups: omnivore n = 27, lacto ovo vegetarian n=27, and vegan n = 28. Participants characteristics are shown in Table 1. Vegan participants were significantly older (33.9 ± 8.6 year versus 27.2 ± 6.7 year respectively) than the omnivores, while the mean age of the lacto ovo vegetarians fell between the two other groups (31.1 ± 9.1 year). Physical activity level or anthropometric measurements did not differ significantly between groups although omnivores displayed the highest body mass index (23.5 ± 3.1 kg/m2, p = 0.092). The vegan diet was found to have the highest rating of diet quality, as shown by the REAP score which was statistically higher than the other groups (36.1 ± 2.0 vs 32.4 ± 2.7 and 31.8 ± 3.2 respectively for the vegans, lacto ovarians, and omnivores). All of the other participant characteristics were not found to be statistically significant with p values over

14 7

15 Although the BMD was reduced 4 5% in individuals who followed a vegan or vegetarian diet, this was not statistically significant and there was no significant variation in BMD between the three diet groups (p = 0.384, Table 2). Z scores were also not significantly different between the three groups. Values that were statistically significantly include calcium excretion, which was higher in the omnivores, and several markers of acid base status (Table 2). Calcium excretion was ~34% higher in meat based diets, with a p value of Urinary ph was more alkaline in the meatless diets versus omnivores, 6.2 ± 0.4 for the omnivores, versus 6.5 ± 0.4 and 6.7 ± 0.4 for the lacto ovo vegetarian and vegan groups. PRAL, another marker of acid base status and significantly related to urinary ph (r = 0.322, p=0.0004), was found to be reduced over 100% in the meatless group compared to the omnivore group, p=0.001). The anion gap was not found to be statistically different between groups. 8

16 9

17 Among the diet groups, there was variation in the intake of nutrients thought to positively affect bone health (Table 3). Protein intake was found to be reduced 30% in individuals adhering to a vegetarian diet, compared to meat based diets (p=0.006, Table 3). Magnesium, folate, and vitamin K consumption was found to be higher in vegetarians and vegans and was statistically significant, while vitamin B12 was significantly higher in meat based diets (Table 3). All other nutrients did not have statistically significant p values. 10

18 11

19 Statistically significant associations were found between BMD and urinary ph in omnivores, and protein consumption and BMD in vegans (Table 4). No other associations were noted between BMD and any specific nutrient, in either diet group. Table 4. Correlation coefficients for urinary ph and protein significantly correlated with BMD in at least one diet group. 12

20 Discussion Our hypothesis was that plant based diets would be associated with a more alkaline acid base profile than omnivorous diets, and thus have a higher bone mineral density. Our present study showed that there was no significant variation in BMD between the three diet groups, although the urinary ph was more alkaline for those adhering to meatless diets (Table 2). A review of the literature shows that there are a few possible explanations for our findings. Bone metabolism is a dynamic and sensitive system, where alterations in either ph or specific nutrients will tip the balance to either more resorption or formation of bone. 10, 27, 15 In this present study, protein intake amongst vegans and lacto ovo vegetarians was reduced by about 30% in comparison to omnivores. Several studies suggest that protein is important for insulin like growth factor I (IGF I) to induce activation of osteoblasts, and thus protein deficiency prohibits the positive effects of IGF I on cortical bone. 11, 12 A double blinded, randomized, placebo controlled trial by Schürch et al. showed that protein supplementation increased IGF I levels and slowed the loss of BMD and even resulted in shorter hospital stay in elderly patients with hip fractures. 11 A cohort study by Thorpe et al. showed that vegetarians with the lowest vegetable protein intake were at high risk for fractures, and simply increasing their protein levels in diet could result in a 68% reduction in risk. 14 On the other hand, several studies suggest that while protein is crucial for bone health 13, it also contributes to the dietary acid load, a product of the oxidation of sulfur amino acids methionine and cysteine, which can adversely affect bone integrity. 16, 10 An acidic extracellular ph promotes osteoclast activation leading to bone resorption, and inhibits osteoblast mediated mineralization of bone. 10 This state of acidosis causes the release of alkaline bone minerals, in order to balance the hydrogen ions created by the diet, specifically the high acid load created by high animal consumption. 10, 28 This release of alkaline bone minerals can cause hypercalcuria 10, which our findings support. Calcium excretion was ~34% higher in meat based diets and was statistically significant. Perhaps that is why urinary ph was associated with bone mineral density only in those following a meat based diet in our study. PRAL, another marker of acid base status 19, 20, was significantly related to urinary ph and was found to be significantly more alkaline in the meatless group. Since PRAL takes into consideration the ionic balance of 13

21 phosphorous, potassium, magnesium, and calcium as well as protein metabolism, it is unsurprising that the PRAL was much more alkaline in our meatless diet groups since they had a higher consumption of those nutrients. A negative PRAL indicates a more alkaline load, and a positive PRAL indicates a higher acid load 31. It is also accepted that diet influences urinary ph. 19, 20, 28, 30 Several studies suggest that neutralization of acid producing Western diets through the use of potassium citrate, or other alkali substance, can increase bone mass. 22, 23, 24 However, a study by Macdonald et al. suggests that alkali provision using potassium citrate supplementation does not explain the benefit of a diet high in fruit and vegetable consumption since they were unable to increase bone mineral density in post menopausal women with two years of potassium citrate supplementation, perhaps because potassium citrate works best in an environment with insufficient calcium intake. 24 The Western diet is high in animal products and deficient in fruits and vegetables necessary to have an alkalinizing effect. 21 In addition to providing metabolizable anions, such as citrate and malate, plant protein is also higher in glutamate, an amino acid that consumes hydrogen ions through its metabolism. 21 In contrast, animal proteins and certain grains have a high content of sulfate, which contributes to the high acid load seen; interestingly, meat and eggs have a two to five hold higher content of sulfate than do grains and legumes. 21 Vitamin K, a nutrient seen specifically in green leafy vegetables 26, has been shown to have a direct effect on bone metabolism 25, by inhibiting bone resorption through its inhibition of osteoclasts and enhancement of osteoblast mineralization. Thus, the similar bone mineral density found amongst the three diet groups can perhaps be explained by the cancelling effect occurring by the positive and negative attributes of each diet. Because in our study vegans lacked protein, which is considered bone negative, but had a more alkaline profile, which is bone positive, that may have led to a net balance of zero. Conversely, meat based diets had sufficient protein, which is bone positive, but had an increased acid load, which is bone negative, that may have led to a net balance of zero, and thus a similar bone mineral density amongst the meat less versus meat based diets. The results of this cross sectional study further support that bone is sensitive to nutrient availability, in addition to the body s acid load. The significance of this study is that it provides 14

22 knowledge in the area of osteoporosis prevention and perhaps specific recommendations based on diet groups: increased fruit and vegetable intake for those with high meat consumption, to improve the acid base homeostasis, and increased plant protein intake for individuals who follow a plant based diet. In addition, it highlights the role that diet plays in acid base homeostasis, and the importance of sufficient fruit and vegetable consumption. Studies suggest that mild acidosis might contribute to insulin resistance and the development of type 2 diabetes 31, increase the risk of cardiovascular disease 28, or even increase the risk of cancer by molecular effects at the cellular level that promote tumor growth. 30 In summary, the vegetarian and vegan diets in young adults did not appear to be detrimental to bone health as sometimes thought 15, but instead might offer protective benefits not only in bone health but also in prevention of chronic diseases. 28 Limitations of this study include the fact that the cross sectional study design can only suggest the possible role that specific diet groups have on bone mineral density. The selfreported dietary log, narrow age window, which inhibits providing insight for older adults or the elderly, and lack of site specific measurements of BMD are also limiting factors of the study. In addition, the fact that the human diet is extremely complex and includes differences such as the variation in nutrient composition, lifestyle factors, and influence of hormones, limits dietary data interpretation. However, a trained nutritionist performed the 24 hour diet recalls, strengthening their validity Future directions for this study include studying the effects of supplemental protein in vegans and vegetarians and seeing the effect on BMD, and conversely, examining whether increased consumption of fruits and vegetables favors bone formation in omnivores. In conclusion, bone is a dynamic and sensitivity entity with response to lack of protein and/or high acid load. The significance of our study is that it highlights specific recommendations for each diet group, in hopes of preserving their bone mineral density and help against the epidemic of osteoporosis. 15

23 References 1. Ilich JZ, Kerstetter JE. Nutrition in bone health revisited: A story beyond calcium. J Am Coll Nutr. 2000;19(6): MacLeay JM, Olson JD, Enns RM, et al. Dietary induced metabolic acidosis decreases bone mineral density in mature ovariectomized ewes. Calcif Tissue Int. 2004;75(5): Tucker KL, Hannan MT, Chen H, Cupples LA, Wilson PW, Kiel DP. Potassium, magnesium, and fruit and vegetable intakes are associated with greater bone mineral density in elderly men and women. Am J Clin Nutr. 1999;69(4): New SA. Do vegetarians have a normal bone mass? Osteoporos Int. 2004;15(9): Key TJ, Appleby PN, Rosell MS. Health effects of vegetarian and vegan diets. Proc Nutr Soc. 2006;65(1): Deriemaeker P, Aerenhouts D, Hebbelinck M, Clarys P. Nutrient based estimation of acidbase balance in vegetarians and non vegetarians. Plant Foods Hum Nutr. 2010;65(1): Domrongkitchaiporn S, Pongskul C, Sirikulchayanonta V, et al. Bone histology and bone mineral density after correction of acidosis in distal renal tubular acidosis. Kidney Int. 2002;62(6): Wynn E, Krieg MA, Lanham New SA, Burckhardt P. Postgraduate symposium: Positive influence of nutritional alkalinity on bone health. Proc Nutr Soc. 2010;69(1): Adeva MM, Souto G. Diet induced metabolic acidosis. Clin Nutr. 2011;30(4): Ahn H, Kim JM, Lee K, Kim H, Jeong D. Extracellular acidosis accelerates bone resorption by enhancing osteoclast survival, adhesion, and migration. Biochem Biophys Res Commun. 2012;418(1): Schurch MA, Rizzoli R, Slosman D, Vadas L, Vergnaud P, Bonjour JP. Protein supplements increase serum insulin like growth factor I levels and attenuate proximal femur bone loss in patients with recent hip fracture. A randomized, double blind, placebo controlled trial. Ann Intern Med. 1998;128(10): Bourrin S, Ammann P, Bonjour JP, Rizzoli R. Dietary protein restriction lowers plasma insulin like growth factor I (IGF I), impairs cortical bone formation, and induces osteoblastic resistance to IGF I in adult female rats. Endocrinology. 2000;141(9):

24 13. Josse AR, Atkinson SA, Tarnopolsky MA, Phillips SM. Diets higher in dairy foods and dietary protein support bone health during diet and exercise induced weight loss in overweight and obese premenopausal women. J Clin Endocrinol Metab. 2012;97(1): Thorpe DL, Knutsen SF, Beeson WL, Rajaram S, Fraser GE. Effects of meat consumption and vegetarian diet on risk of wrist fracture over 25 years in a cohort of peri and postmenopausal women. Public Health Nutr. 2008;11(6): Ho Pham LT, Vu BQ, Lai TQ, Nguyen ND, Nguyen TV. Vegetarianism, bone loss, fracture and vitamin D: A longitudinal study in asian vegans and non vegans. Eur J Clin Nutr. 2012;66(1): Remer T. Influence of nutrition on acid base balance metabolic aspects. Eur J Nutr. 2001;40(5): Lemann J,Jr, Bushinsky DA, Hamm LL. Bone buffering of acid and base in humans. Am J Physiol Renal Physiol. 2003;285(5):F Sebastian A, Harris ST, Ottaway JH, Todd KM, Morris RC,Jr. Improved mineral balance and skeletal metabolism in postmenopausal women treated with potassium bicarbonate. N Engl J Med. 1994;330(25): Michaud DS, Troiano RP, Subar AF, et al. Comparison of estimated renal net acid excretion from dietary intake and body size with urine ph. J Am Diet Assoc. 2003;103(8):1001 7; discussion Thorpe M, Mojtahedi MC, Chapman Novakofski K, McAuley E, Evans EM. A positive association of lumbar spine bone mineral density with dietary protein is suppressed by a negative association with protein sulfur. J Nutr. 2008;138(1): Adeva MM, Souto G. Diet induced metabolic acidosis. Clin Nutr. 2011;30(4): Jehle S, Zanetti A, Muser J, Hulter HN, Krapf R. Partial neutralization of the acidogenic western diet with potassium citrate increases bone mass in postmenopausal women with osteopenia. J Am Soc Nephrol. 2006;17(11): Jehle S, Hulter HN, Krapf R. Effect of potassium citrate on bone density, microarchitecture, and fracture risk in healthy older adults without osteoporosis: A randomized controlled trial. J Clin Endocrinol Metab. 2013;98(1):

25 24. Macdonald HM, Black AJ, Aucott L, et al. Effect of potassium citrate supplementation or increased fruit and vegetable intake on bone metabolism in healthy postmenopausal women: A randomized controlled trial. Am J Clin Nutr. 2008;88(2): Shiraki M, Shiraki Y, Aoki C, Miura M. Vitamin K2 (menatetrenone) effectively prevents fractures and sustains lumbar bone mineral density in osteoporosis. J Bone Miner Res. 2000;15(3): Gunn CA, Weber JL, Coad J, Kruger MC. Increasing fruits and vegetables in midlife women: A feasibility study. Nutr Res. 2013;33(7): Campbell WW, Barton ML,Jr, Cyr Campbell D, et al. Effects of an omnivorous diet compared with a lactoovovegetarian diet on resistance training induced changes in body composition and skeletal muscle in older men. Am J Clin Nutr. 1999;70(6): Schwalfenberg GK. The Alkaline Diet: Is There Evidence That an Alkaline ph Diet Benefits Health? Journal of Environmental and Public Health. 2012;2012: Lanham New SA. Is "vegetarianism" a serious risk factor for osteoporotic fracture? Am J Clin Nutr. 2009;90(4): Robey IF. Examining the relationship between diet induced acidosis and cancer. Nutrition & Metabolism. 2012;9: Williams RS, Heilbronn LK, Chen DL, Coster AC, Greenfield JR, Samocha Bonet D. Dietary acid load, metabolic acidosis and insulin resistance lessons from cross sectional and overfeeding studies in humans. Clin Nutr