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Dean Pomerleau posted a topic in CR PracticeAll, The idea that rapid weight loss can result in release of toxins stored (relatively harmlessly) in body fat cells gets bandied about pretty regularly. In fact I've done it myself several times in just the last couple days (here and here). I've never actually looked for evidence to support this conventional wisdom, which has left me with a nagging feeling of dis-ease. I try not to make claims that I can't back up with evidence. So I figured I would look into it and start a new thread to collect the evidence and encourage discussion about it. Coincidently (or perhaps not?!), Al Pater posted this new study  today, which bears directly on the topic. In it, researchers followed 32 women who had just given birth and were breast feeding to see how the level of persistent organic pollutants (POPs) in their breast milk changed as a function of postpartum weight loss. All the women lost at least some weight in the 24 weeks of the study, and sure enough, the amount of POPs in their breast milk was highly correlated with the amount of weight they lost: Among these women, the concentration of PCB 153 in HM was significantly (p = 0.04) higher at follow-up than at baseline. Weight loss was significantly positively associated with changes in concentrations of all studied POPs (2.0-2.4% increase per percent weight loss). Since these women probably weighed in the neighborhood of 140-180 lbs to start with, it appears that the level of toxins in their breast milk went up by about 1-2% per pound of weight loss. Since not all of the toxins released end up in breast milk (especially in men and non-lactating women!) I would expect the increase in toxin load circulating in the blood per pound of weight loss to be higher than that. So  definitely supports the idea that rapid weight loss increases circulating toxin load. But even more direct and conclusive evidence of dieting-induced toxin release is study . In , researchers followed 45 morbidly obese women for 6 months following either bariatric surgery or intensive dieting. These women were really heavy to start with - average BMI around 40. And they lost quite a bit of weight (-32lbs of body weight on average) in a relatively short period of time (six months). But in fact that translates into 1.23lbs per week of weight loss, which is very close to the maximum rate of weight loss we recommend around here, ~1lb per week. So what did they find? A very large increase in the same Persistent Organic Pollutants (POPs), to the tune of a 50% increase on average: In patients who lost weight, serum [total POP] levels displayed an increase after 6 months of approximately 50%. ... [T]he increase in [Total POP] serum levels after 6 months of weight loss was more pronounced in patients losing relatively more visceral adipose tissue. So even the kind of "slow-and-steady" weight loss we recommend of 1lb of weight per week results in a dramatic increase in toxin load that persists for at least six months. And visceral fat loss is a bigger factor contributing to toxin release than subcutaneous (love-handle) fat loss. In satisfying agreement with the 1-2% increase in POPs per pound of weight loss observed in , this study found that an average of 32lbs of weight loss resulted in a 50% increase in average serum POP level, which equates to ~1.5% increase in circulating POPs per pound of weight loss. So in general even 1lb of weight loss per week may be too rapid... Ah. That feels better. My cognitive dissonance is subsiding... Now I can go back to those two posts and insert a link to this thread. And now we have a place to point next time anyone makes the statement that rapid weight loss releases toxins into the blood. --Dean ------------  Chemosphere. 2016 Jun 6;159:96-102. doi: 10.1016/j.chemosphere.2016.05.077. Environmental organic pollutants in human milk before and after weight loss. Lignell S, Winkvist A, Bertz F, Rasmussen KM, Glynn A, Aune M, Brekke HK. Abstract Many persistent organic pollutants (POPs) are banned because they accumulate in organisms and are toxic. Lipophilic POPs are stored in maternal adipose tissue and concentrations in human milk (HM) may increase during weight loss. Our aim was to examine associations between weight loss and concentrations of chlorinated POPs in HM in lactating women participating in a weight loss study. We analysed POPs (PCB 28, PCB 153, HCB, DDE) in HM at 12 and 24 weeks postpartum from 32 women who participated in a randomized, 2 ? 2 factorial trial of diet and exercise for postpartum weight loss. Participants donated milk before and after the intervention period. We examined associations between weight loss and change in POP concentrations and estimated the intake of POPs by their breastfed infants. Most (n = 27) women lost weight during intervention, 0.45?0.30 kg/week (mean?SD). Among these women, the concentration of PCB 153 in HM was significantly (p = 0.04) higher at follow-up than at baseline. Weight loss was significantly positively associated with changes in concentrations of all studied POPs (2.0-2.4% increase per percent weight loss). Estimated mean intakes of POPs (ng/day) remained stable because infant milk consumption decreased during the study period. As infants gained weight, estimated mean intakes per kg body weight decreased 17-22%. Changes in concentrations of POPs in HM correlated positively with maternal weight loss, but it is unlikely that the balance between the benefits and risks of breastfeeding will change if the weight loss is restricted to 0.5 kg per week. KEYWORDS: Human milk; Obese; Overweight; POPs; Postpartum; Weight loss PMID: 27281542 ------------  J Clin Endocrinol Metab. 2015 Dec;100(12):4463-71. doi: 10.1210/jc.2015-2571. Epub 2015 Oct 15. Pivotal Role for the Visceral Fat Compartment in the Release of Persistent Organic Pollutants During Weight Loss. Dirinck E(1), Dirtu AC(1), Jorens PG(1), Malarvannan G(1), Covaci A(1), Van Gaal LF(1). Author information: (1)Department of Endocrinology, Diabetology, and Metabolism (E.D., L.F.V.G.), Toxicology Centre (A.C.D., G.M., A.C.), and Department of Intensive Care Medicine/Clinical Pharmacology (P.G.J.), Antwerp University Hospital, University of Antwerp, 2650 Edegem, Belgium. Full text: http://sci-hub.cc/10.1210/jc.2015-2571 CONTEXT: Polychlorinated biphenyls (PCBs), are implicated as potential endocrine disruptors and obesogens. These lipophilic substances are preferentially stored in the fat compartment and released into the circulation during weight loss. OBJECTIVE: The aim of this study was to examine the contribution of abdominal adiposity, and visceral adiposity in particular, to the increase of serum PCB levels during weight loss. MATERIALS AND METHODS: Fourty-five obese women were prospectively recruited. Twenty individuals received dietary counseling and 25 underwent bariatric surgery. Anthropometric data were collected and intra-abdominal adiposity was assessed by measurement computed tomography scanning of the abdominal fat compartment, delineating the visceral and subcutaneous compartment. Serum levels of 27 PCBs were determined and the sum of all PCBs (ΣPCBs) calculated. Follow-up measurements of anthropometric data, computed tomography scanning, and PCB levels were performed after 6 months in all patients. RESULTS: In patients who lost weight, serum ΣPCB levels displayed an increase after 6 months of approximately 50%. Both correlation and regression analysis, focusing on the relative contribution of the visceral vs the subcutaneous fat compartment, suggested that the increase in ΣPCB serum levels after 6 months of weight loss was more pronounced in patients losing relatively more visceral adipose tissue. This trend could be established in the diet-treated, but not the surgery-treated subgroup. CONCLUSION: Our study suggests that the contribution of PCBs released from the visceral fat compartment might be more pronounced compared with the subcutaneous fat compartment during weight loss. These findings are present in the entire study group whereas subanalysis of the diet vs surgery groups suggested the same effect in the diet group but failed to reach statistical significance in the surgery group. This suggests a possible weight-loss method-specific effect. PMID: 26469381