Thursday, June 19, 2008

Extreme low carb and thyroid studies

Another post stolen from Lyle's board

J Endocrinol Invest. 1982 Jan-Feb;5(1):47-52.Links
Effect of dietary carbohydrates during hypocaloric treatment of obesity on peripheral thyroid hormone metabolism.
Pasquali R, Parenti M, Mattioli L, Capelli M, Cavazzini G, Baraldi G, Sorrenti G, De Benedettis G, Biso P, Melchionda N.

The effect of different hypocaloric carbohydrate (CHO) intakes was evaluated in 8 groups of obese patients in order to assess the role of the CHO and the other dietary sources in modulating the peripheral thyroid hormone metabolism. These changes were independent of those of bw. Serum T3 concentrations appear to be more easily affected than those of reverse T3 by dietary manipulation and CHO content of the diet. A fall in T3 levels during the entire period of study with respect to the basal levels occurred only when the CHO of the diet was 120 g/day or less, independent of caloric intake (360, 645 or 1200 calories). Moreover, reverse T3 concentrations were found increased during the entire period of study when total CHO were very low (40 to 50 g/day) while they demonstrated only a transient increase when CHO were at least 105 g/day (with 645 or more total calories). Indeed, our data indicate that a threshold may exist in dietary CHO, independent of caloric intake, below which modifications occur in thyroid hormone concentrations. From these results it appears that the CHO content of the diet is more important than non-CHO sources in modulating peripheral thyroid hormone metabolism and that the influence of total calories is perhaps as pronounced as that of CHO when a "permissive" amount of CHO is ingested.

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and the National Institutes of Health

1: Metabolism. 1986 May;35(5):394-8.
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The effect of varying carbohydrate content of a very-low-caloric diet on resting metabolic rate and thyroid hormones.

Mathieson RA, Walberg JL, Gwazdauskas FC, Hinkle DE, Gregg JM.

Twelve obese women were studied to determine the effects of the combination of an aerobic exercise program with either a high carbohydrate (HC) very-low-caloric diet (VLCD) or a low carbohydrate (LC) VLCD diet on resting metabolic rate (RMR), serum thyroxine (T4), 3,5,3'-triiodothyronine (T3), and 3,5,3'-triiodothyronine (rT3). The response of these parameters was also examined when subjects switched from the VLCD to a mixed hypocaloric diet. Following a maintenance period, subjects consumed one of the two VLCDs for 28 days. In addition, all subjects participated in thrice weekly submaximal exercise sessions at 60% of maximal aerobic capacity. Following VLCD treatments, participants consumed a 1,000 kcal mixed diet while continuing the exercise program for one week. Measurements of RMR, T4, T3, and rT3 were made weekly. Weight decreased significantly more for LC than HC. Serum T4 was not significantly affected during the VLCD. Although serum T3 decreased during the VLCD for both groups, the decrease occurred faster and to a greater magnitude in LC (34.6% mean decrease) than HC (17.9% mean decrease). Serum rT3 increased similarly for each treatment by the first week of the VLCD. Serum T3 and rT3 of both groups returned to baseline concentrations following one week of the 1,000 kcal diet. Both groups exhibited similar progressive decreases in RMR during treatment (12.4% for LC and 20.8% for HC), but values were not significantly lower than baseline until week 3 of the VLCD. Thus, although dietary carbohydrate content had an influence on the magnitude of fall in serum T3, RMR declined similarly for both dietary treatments.

Publication Types:

* Research Support, U.S. Gov't, P.H.S.

PMID: 3702673 [PubMed - indexed for MEDLINE]

2: Metabolism. 1980 Aug;29(8):721-7.
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Thyroid hormone homeostasis in states of relative caloric deprivation.

O'Brian JT, Bybee DE, Burman KD, Osburne RC, Ksiazek MR, Wartofsky L, Georges LP.

Starvation is accomplished by significant changes in the hypothalamic-pituitary-thyroid axis and in peripheral thyroid hormone metabolism. Less well studied, however, are the effects on thyroid hormone economy produced by hypocaloric feeding. We explored these changes in obese patients fed 200, 400, or 600 cal/day of either carbohydrate of protein for 28 days. T4' T3' reverse T3 and the TSH response to TRH were measured at frequent intervals. Each patient demonstrated a transient rise in reverse T3 and a fall in T2 that returned to near basal levels by the end of the study period. The TSH response to TRH on the other hand, declined to approximately 50% of control values and remained at that level throughout the course of study, regardless of the type of substrate or calorie level chosen. The results indicated that hypocaloric feeding is associated with changes in thyroid hormone economy similar to those in starvation and that peripheral (changes in T3 and rT3) and central (TRH response) events are controlled by separate mechanisms.

Publication Types:

* Research Support, U.S. Gov't, Non-P.H.S.

PMID: 6772921 [PubMed - indexed for MEDLINE]

3: J Clin Endocrinol Metab. 1976 Jan;42(1):197-200.
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Effect of caloric restriction and dietary composition of serum T3 and reverse T3 in man.

Spaulding SW, Chopra IJ, Sherwin RS, Lyall SS.

To evaluate the effect of caloric restriction and dietary composition on circulating T3 and rT3 obese subjects were studied after 7-18 days of total fasting and while on randomized hypocaloric diets (800 kcal) in which carbohydrate content was varied to provide from 0 to 100% calories. As anticipated, total fasting resulted in a 53% reduction in serum T3 in association with reciprocal 58% increase in rT3. Subjects receiving the no-carbohydrate hypocaloric diets for two weeks demonstrated a similar 47% decline in serum T3 but there was no significant change in rT3 with time. In contrast, the same subjects receiving isocaloric diets containing at least 50 g of carbohydrate showed no significant changes in either T3 or rT3 concentration. The decline in serum T3 during the no-carbohydrate diet correlated significantly with blood glucose and ketones but there was no correlation with insulin or glucagon. We conclude that dietary carbohydrate is an important regulatory factor in T3 production in man. In contrast, rT3 concentration is not significantly affected by changes in dietary carbohydrate. Our data suggest that the rise in serum rT3 during starvation may be related to more severe caloric restriction than that caused by the 800 kcal diet.

Publication Types:

* Research Support, U.S. Gov't, P.H.S.

PMID: 1249190 [PubMed - indexed for MEDLINE]

4: J Endocrinol Invest. 1983 Apr;6(2):81-9.
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Relationships between iodothyronine peripheral metabolism and ketone bodies during hypocaloric dietary manipulations.

Pasquali R, Baraldi G, Biso P, Pasqui F, Mattioli L, Capelli M, Callivá R, Spoto M, Melchionda N, Labò G.

Relationships between iodothyronine and metabolic substrate metabolism during undernutrition were evaluated in four normal subjects who fasted for 48h (Group I) and in four groups (II to V) of obese patients who underwent selective dietary manipulations: 360 calories [carbohydrate (CHO) 40 g/day]; 800 calories containing respectively 19 g/day - ketogenic - (K) and 112 g/day - non ketogenic - (NK) of CHO; and a step-diet programme (during which total calories were progressively reduced from 2500 to 500). Serum T3 levels decreased significantly and constantly during fasting, 360 and 800 K studies, and transiently during the 800 NK diet. During the step-diet programme, a significant fall was found only when 1250 K or less were given. Conversely, serum reverse T3 rose significantly and constantly during 360 and 800 K diets, while a transient increase was found during the 800 NK diet. During the step-diet programme reverse T3 rose only when 750 calories were given. Ketogenesis developed in all studies but one (800 NK), and in the step-diet programme significantly below the 1000 calorie step. Other substrate modifications in each study were also evaluated. Serum T3 levels showed a significant correlation with ketone bodies (KB) in all the ketogenic studies, while no correlation was found in non ketogenic study (800 NK). During the step-diet programme ketone bodies and iodothyronine modifications appeared to be related to the amount of calories. Based on these results, we suggest a relationship between the dietary-induced modifications of iodothyronine metabolism and the development of ketogenesis.

Publication Types:

* Comparative Study

PMID: 6863849 [PubMed - indexed for MEDLINE]

5: Metabolism. 1983 Jan;32(1):9-13.
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Adaptation to hypocaloric feeding: physiologic significance of the fall in serum T3 as measured by the pulse wave arrival time (QKd).

Osburne RC, Myers EA, Rodbard D, Burman KD, Georges LP, O'Brian JT.

We have investigated the physiologic significance of the decline in serum triiodothyronine (T3) occurring during hypocaloric feeding by measurement of changes in cardiovascular function. The QKd interval, the interval between the Q wave of the electrocardiogram and the onset of Korotkoff sounds at diastolic pressure at the brachial artery, is the sum of the preejection period and pulsetransmission time, and has proven to be a sensitive and effective measure of the effect of thyroid hormones on the cardiovascular system. Fifteen euthyroid obese volunteers underwent successive 2 wk periods of hypocaloric feeding (200-400 calories per day) interspersed with periods of at least 2 wk of re-feeding on a weight-maintaining diet (1500 calories). In a later phase subjects received oral supplementation of triiodothyronine (T3) in addition to the diet to prevent the fall in serum T3. In the last study phase, subjects on the diet received supplementation with oral thyroxine (T4), which prevented the fall in serum T3 and resulted in a slight increase in serum T4. During the first 2 wk period of hypocaloric feeding, there was a statistically significant increase in QKd, and a decrease in pulse rate, compatible with a hypothyroid state relative to initial measurements. When oral T3 supplementation was given, the rise in QKd and fall in pulse rate were prevented. Likewise, with oral T4 supplementation, the changes in QKd and pulse were prevented. Thus, the fall in serum T3 occurring during hypocaloric feeding is associated with changes in the cardiovascular system which are qualitatively similar to those observed during hypothyroidism. The present data, taken with other data in the literature, suggest that the decline in serum T3 during hypocaloric feeding may be an adaptive mechanism to conserve energy during caloric deprivation.

Publication Types:

* Research Support, Non-U.S. Gov't

PMID: 6848901 [PubMed - indexed for MEDLINE]

6: Metabolism. 1980 Oct;29(10):930-5.
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Click here to read
The role of dietary fat in peripheral thyroid hormone metabolism.

Otten MH, Hennemann G, Docter R, Visser TJ.

Short term changes in serum 3,3',5-triiodothyronine (T3) and 3,3'5-triiodothyronine (reverse T3, rT3) were studied in four healthy nonobese male subjects under varying but isocaloric and weight maintaining conditions. The four 1500 kcal diets tested during 72 hr, consisted of: I, 100% fat; II, 50% fat, 50% protein; III, 50% fat, 50% carbohydrate (CHO), and IV, a mixed control diet. The decrease of T3 (50%) and increase of rT3 (123%) in the all-fat diet equalled changes noted in total starvation. In diet III (750 kcal fat, 750 kcal CHO) serum T3 decreased 24% (NS) and serum rT3 rose significantly 34% (p < 0.01). This change occurred in spite of the 750 kcal CHO. This amount of CHO by itself does not introduce changes in thyroid hormone levels and completely restores in refeeding models the alterations of T3 and rT3 after total starvation. The conclusion is drawn that under isocaloric conditions in man fat in high concentration itself may play an active role in inducing changes in peripheral thyroid hormone metabolism.

Publication Types:

* Comparative Study

PMID: 7421583 [PubMed - indexed for MEDLINE]

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