Sunday, April 29, 2012

Calcium In, Calcium Out

Calcium Intake

Osteoporosis is thought to be due to a negative calcium balance. It’s suggested that a low dietary intake of calcium and/or low vitamin D levels reduces the amount of calcium absorbed, which then increases parathyroid hormone level to maintain calcium levels by through bone resorption.

While calcium deficiency may cause osteoporosis, randomised controlled trials of calcium supplements don't show too much benefit for fracture rates and have increased the number of cardiovascular events, but not total mortality.


Fracture Rates
Heart Attacks
Total
CVD
Meta-Analysis of RCTs (institutionalised) [1]
Calcium and Calcium + Vitamin D
-24%


Meta-Analysis of RCTs (community) [1]
Calcium and Calcium + Vitamin D
-6%


Meta-Analysis of RCTs [2]
Calcium (women/men)
-8/-6%


Meta-Analysis of RCTs [3]
Calcium and Calcium + Vitamin D

+24%
+15%
Meta-Analysis of RCTs [4]
Calcium

+31%
+18%*
* Non-significant

Calcium and calcium + vitamin D supplementation in studies that were institutionalised and/or had high compliance rates reduced fracture rates by 24% compared with only 6% in RCTs that were community based (low compliance). Other factors that influence the effect size of calcium supplementation include age and baseline dietary calcium intake. The studies with higher compliance do a better job of reflecting the actual effect of calcium supplementation, so I’ll rather use that data. The authors discuss that there seems to be some publication bias, but not enough to suggest calcium supplementation has no effect on fracture rates [1]. So I’m comfortable in concluding that calcium supplements seem to reduce overall fracture rates by approximately 20%.

However, it’s clear that the proposed mechanism that’s mentioned above (low calcium absorbed >> low serum calcium>> increase parathyroid hormone >> bone resorption) is hardly the full story. Calcium supplements raise serum calcium even more strongly than dietary calcium [5], but this only slows down bone loss, admittedly by about 50% [6]. While a 20% reduction in fractures sounds good, altogether this suggests that some other mechanism is being overlooked and perhaps calcium is simply covering up the problem.

* Elevated serum calcium levels and hyperparathyroidism are associated with an increased risk of cardiovascular disease, which may explain why calcium supplementation increases the risk [4]. The risk of supplemental calcium is related to kidney function. Food forms of calcium such as dairy and bone don’t elevate serum calcium as much as supplements do [5]

** The Women’s Health Initiative trial found that among people not taking calcium at randomisation, calcium and vitamin D supplementation reduced cancer by 14% [7]

*** Vitamin D supplementation of 700-1,000 IU reduces falls by 19% [8]

Calcium Out: The Dietary Acid-Base Theory of Osteoporosis

An alternative theory of osteoporosis is that high dietary acid loads (mainly from protein, particularly the sulphur amino acids, and phosphorus, both of which animal foods are rich in) cause the body acidic and then calcium (which is alkaline) is leeched from the bones and used to balance the acid load on the kidneys.  Vegetarians and vegans use this as an argument against meat, while early versions of Paleo used this as an argument against dairy.

However, contrary to the dietary acid-base theory of osteoporosis:

  • Calcium isn’t leeched due to lower renal pH
  • Calcium balance isn’t affected by minor physiological changes in pH (7.35-7.45)
  • Protein doesn’t decrease bone mineral density and low protein is not ideal for bone health
  • Alkaline diets and supplements don’t increase bone mineral density or markers of bone formation [9]

“A causal association between dietary acid load and osteoporotic bone disease is not supported by evidence and there is no evidence that an alkaline diet is protective of bone health.” [9]

Furthermore, high protein diets maintain calcium balance as they increase calcium absorption and excretion. There was no difference in bone resorption or bone formation biomarkers between the high protein and low protein diet. The high protein diet increased IGF-1 and decreased parathyroid hormone, which could suggest high protein diets promote bone health* [10]. Also in the Framingham study** found that those who ate the most protein had the highest bone mineral density [11]

A likely reason why dietary acid-base theories have little evidence to support them is because our body’s pH is tightly regulated between 7.38-7.42 (lower pH is more acidic, higher pH is more alkaline and a pH of 7 is neutral) and the main regulatory mechanisms don’t involve calcium.  To regulate pH we have the bicarbonate buffering system, which converts carbon dioxide (acidic) and water to carbonic acid (acidic), carbonic acid to bicarbonate (alkaline) and a hydrogen ion (acidic), and vice versa.

CO2 + H2O <> H2CO3 <> HCO3- + H+

From here, pH homeostasis is achieved in the short term by the lungs regulating the amount of CO2 in the bloodstream, and long term by the kidneys regulating the amount of bicarbonate and hydrogen ions (as well as other acidic and basic molecules) that are excreted and reabsorbed

Rather than pathologise the modest amount of protein in the SAD, it’s more informative to look at actual causes of acidity, which can arise from a defect in the regulatory systems – respiratory acidosis or metabolic acidosis due to poor kidney function – or other sources of metabolic acidosis where the regulatory systems being overwhelmed, such as ketoacidosis (due to insulin deficiency, not ketosis) and lactic acidosis (due to hypoxia or mitochondrial dysfunction)

* Seeing as the high protein diet lowered parathyroid hormone it seems likely that protein increases calcium absorption primarily and then increases calcium excretion simply because there’s excess calcium in the blood. If protein increased calcium absorption to compensate for increased calcium excretion/low serum calcium then parathyroid hormone would go up

** Data from the Framingham study suggests people with a more alkaline diet (more fruit, vegetables, potassium and magnesium) had higher bone mineral density and lower bone loss over time [11]. However, this (and similar findings) doesn’t prove the alkaline hypothesis, as the major confounding variable is that fruit and vegetables are healthy anyway, and potassium and magnesium intake could be markers of a better diet. There would need to be evidence for alkaline diets independent of the other biological effects of fruit, vegetables and alkaline supplements.

Further Reading:
(1) The Acid-Alkaline Myth: Part 1
(2) The Acid-Alkaline Myth: Part 2
(3) Calcium Supplements: Why You Should Think Twice
(4) Does Dairy Cause Osteoporosis?

Sunday, April 22, 2012

Bones

Bone Mineral Density vs. Bone Fractures 

Bone mineral density is used to diagnose osteoporosis.  Normal bone mineral density is considered less than or equal to 1 standard deviation below the mean bone mineral density of 30 year old men and women.  Osteopenia is diagnosed when between 1 to 2.5 standard deviations below the mean and osteoporosis is diagnosed when greater than or equal to 2.5 standard deviations below the mean.

Normal Bone

Osteoporotic Bone
Discussions about osteoporosis are largely concerned with bone mineral density, but the actual end-point we want to avoid are the bone fractures.  Normally bone mineral density is related to fractures, but sometimes bone mineral density is affected strongly without having much impact on fracture rates and vice versa.  Ironically, having excessive bone mineral density due to osteopetrosis (a rare inherited disorder and an uncommon side effect of bisphosphonates (a class of drugs used to treat osteoporosis)) can actually increase the risk of bone fractures. For these reasons I’ll use fracture rates over bone mineral density wherever possible 

Bone Formation and Resorption 

Bones are much more than calcium, it is living tissue.  It’s important to know a little about bones to understand osteoporosis.


Osteoblasts are like bone stem cells that are responsible for bone formation.  They produce a matrix of osteoid, which is the unmineralised, organic part of bone, made mostly of collagen, and produce osteocalcin, which is a mineral binding protein to help mineralise osteoids.  When osteoids are mineralised they become osteocytes, the most common cell in bone.  I’ll refer to this process as bone formation. 

Osteoclasts break down bone tissue and release the bound minerals in a process called bone resorption.  Bones have a natural turnover rate – osteoclasts break down damaged bone cells and osteoblasts form fresh bone cells.  Osteoclasts are important as this process is necessary to adapt to exercise, recover from damage, remove old cells and maintain calcium homeostasis [1]. 

Like adipocytes (fat cells) and myocytes (muscle cells), osteocytes also regulate their growth by using a negative feedback system.  Osteocytes produce a protein called sclerostin, which inhibits further bone formation. 

Cell
Negative Regulator of Growth
Adipocytes
Leptin
Myocytes
Myostatin
Osteocytes
Sclerostin

One function of bone turnover is to maintain calcium homeostasis.  Calcium is necessary for neurotransmitter release, muscle contraction, etc.  Serum calcium levels is tightly regulated by two main hormones: parathyroid hormone and calcitonin.  Parathyroid hormone is released in response to low serum calcium to increase it by stimulating osteoclasts to break down bone and release calcium, activating vitamin D (to 1,25-hydroxyvitamin D) to increase calcium absorption in the intestine and increase reabsorption in the kidneys.  Calcitonin is released in response to high serum calcium to decrease it by decreasing osteoblast activity, calcium absorption and reabsorption (essentially the opposite of parathyroid hormone). 

This may lead one to think that osteoclasts and parathyroid hormone are ‘bad’ while osteoblasts and calcitonin are ‘good’.  Remember that both bone remodelling and calcium homeostasis is important – all four are ‘good’ in the right amount.  Osteoporosis is likely due to too little osteoblast activity (bone formation) and/or too much osteoclast activity (bone resorption).  Hyperparathyroidism, which may be caused by cancer, vitamin D deficiency and kidney failure, can lead to osteoporosis.  But intermittent pulses of parathyroid hormone (the normal physiological condition) actually improve bone mineral density and bone quality by increasing IGF-1, preventing osteoblast apoptosis and inhibiting sclerostin [1].

Sunday, April 15, 2012

Obesity

Summary
 
The thrifty gene hypothesis (feast and famine) suggests some people have thrifty genes that promote overeating and weight gain during times of plenty to prepare them for famines and that because famines no longer occur these people gain weight.
 
There are some problems with the thrifty gene hypothesis:
 
  • Hunter-gatherers maintain a stable and healthy body weight, despite rarely experiencing famines
  • During a famine, infectious disease and plant toxins kill more people than starvation
  • People can lose weight on ad libitum diets
  • Obese people use energy less efficiently
 
Calories in, calories out is true.  If you eat more calories than you expend you will gain weight and if you eat fewer calories than you expend you will lose weight.  But the real question is what makes some people overeat?
 
  • The low fat approach suggests fat causes obesity because fat has more calories per gram than carbs and protein, making it more energy dense
  • The low carb approach suggests carbohydrates cause obesity because carbohydrates increase insulin and insulin promotes fat storage
  • The low fructose approach suggests fructose is a toxin that is metabolised like alcohol, is converted to fat and causes obesity by firstly causing insulin resistance.
 
Yet people on both low fat and low carb diets spontaneously reduce their calories and lose more weight than those on calorie restricted diets.  Like CICO, the low fat argument doesn’t appreciate the role of satiety hormones and the low carb and low fructose mechanisms have counter evidence against them.  While the reasoning as to why these diets work is poor, it doesn’t mean they can’t be successful weight loss approaches.
 
Leptin is a hormone released by fat cells and communicates to the brain as to how much stored fat there is. The brain responds by adjusting appetite and energy expenditure to maintain a body fat setpoint. Leptin resistance is where the brain doesn’t receive as leptin and so thinks there’s less fat stored and compensates through something akin to the starvation response – increasing appetite and decreasing energy expenditure. Leptin resistance precedes and causes obesity. So what causes leptin resistance?
 
Inhibiting signal transduction and decreasing the number of hormone receptors are the major causes of hormone resistance. SOCS3 and PTP1B inhibit the signal transduction of leptin, causing leptin resistance.
 
Lipopolysaccharides >> Inflammation >> SOCS3 >> Leptin resistance
Mitochondrial dysfunction >> ER stress >> PTP1B >> Leptin resistance
 
Inflammation, mitochondrial dysfunction and ER stress can also cause the neurons that leptin signals to maintain weight neuron death to the neurons that receive leptin, which decreases the number of leptin receptors.
 
Some other causes of obesity include food reward, sleep loss and circadian rhythm disruption, and leptin transport.
 
Obesity is a complex disease, there are many factors that can contribute towards it.  There is no one cause of obesity just as there’s no one solution.
 
I prefer to look for problems in the homeostatic mechanisms that would ordinarily protect us from disease.  In the case of obesity that’s essentially leptin resistance.  Leptin resistance can be caused by elevated SOCS3 and PTP1B, which in turn are caused by inflammation and mitochondrial dysfunction/ER stress.  Inflammation and mitochondrial dysfunction/ER stress can also explain the strong associations between obesity and chronic disease.
 
Obesity isn’t a simple matter where discussions ending with calories in, calories out or feast and famine are helpful.  I consider obesity to be a symptom of an underlying pathology (inflammation, mitochondrial dysfunction, etc).  In my opinion, addressing the causes of obesity/weight gain is one of the few paths to sustainable weight loss/maintenance
 
 
Some Strategies for Obesity/Weight Loss/etc
 
This is for informational purposes only and is not meant to diagnose or treat any medical condition.
 
Improve Mitochondrial Function
 
See Mitochondrial Dysfunction (particularly the second half)
 
Reduce Inflammation
 
 
Reduce Food Reward
 
 
Improve Sleep
 

Sunday, April 8, 2012

Some Other Causes of Obesity

Food Reward
 
The food reward hypothesis of obesity suggests that ‘rewarding’ foods (reward being "a process that reinforces behavior") leads to overconsumption of calories and an upregulation of the body fat setpoint.
 
Stephan Guyenet has often discussed food reward.  See Food Reward: a Dominant Factor in Obesity: Part 1, 2, 3, 4, 5, 6, 7 and 8; The Case for the Food Reward Hypothesis of Obesity: Part 1 and 2; Why Do We Eat? A Neurobiological Perspective: Part 5 and 6; and Seduced by Food: Obesity and the Human Brain
 
J Stanton has discussed food reward and related concepts in Why Are We Hungry: Part 1, 2, 3, 4, 5, 6, 7 and 8.  Paul Jaminet has discussed food reward here
 
Some of the difficulties of food reward is that palatability and reward aren’t necessarily inherent properties of food (they can vary from person to person), and the Cafeteria diet is one of the arguments in favour of food reward, but (in my opinion) 28/31 of the foods in the Cafeteria diet are junk food [1], so it’s difficult to tease apart food reward related effects of the Cafeteria diet from other (metabolic/gut/etc) effects of junk food.  That being said, perhaps the main reason people eat junk food is because it’s rewarding/palatable, so food reward can definitely influence people’s choices, which is certainly a relevant issue in the modern food environment.
 
* Food reward is not addiction.  This is discussed in some of the posts I linked
 
Sleep Loss
 
Shorter sleep duration is associated with a higher BMI.  Sleep loss studies tend to find decreases in leptin, increases in ghrelin (a hormone that stimulates appetite) and increased calorie intake [2].  Sleep restriction also increases activity of brain reward centres in response to unhealthy food [3] and increases pro-inflammatory cytokines [4]
 
Sleep can affect how weight is lost during calorie restriction.  In a cross-over study 10 overweight adults did moderate calorie restriction for two blocks of 14 days.  One group was told to sleep for 8.5 hours, the other for 5.5 hours.  Both groups lost the same amount of weight (2.9 vs. 3.0 kg), but with 8.5 hours of sleep they lost approximately 50% lean mass and 50% fat, but with 5.5 hours of sleep they lost 80% lean mass and 20% fat* [5]
 
 
8.5 Hours of Sleep
5.5 Hours of Sleep
Weight Lost as Fat (kg)
1.4
0.6
Weight Lost as Fat-Free Mass (kg)
1.5
2.4
Total Weight Loss (kg)
2.9
3.0
 
Circadian rhythm is also important.  In rats on DIO, dim light during the sleep cycle exaggerates the inflammation and weight gain [6], while timed feeding to promote circadian rhythms almost completely protects against DIO [7]
 
* From this graph you can see 12h sleep group released more leptin than the 8h group and yet most people wouldn’t consider an 8h night to be result in sleep debt [2]. 

 
** A related quote from Stephan Guyenet on the study:
 
“That illustrates one of the reasons why I'm skeptical of simple calorie restriction as a means of fat loss. When the body "wants" to be fat, it will sacrifice lean mass to preserve fat tissue. For example, the genetically obese Zucker rat cannot be starved thin. If you try to put it on a severe calorie-restricted diet, it will literally die fat because it will cannibalize its own lean mass (muscle, heart, brain, etc.) to spare the fat. That's an extreme example, but it illustrates the point.”
 
Impaired Leptin Transport
 
Most the research on leptin resistance discusses SOCS3 and/or PTP1B, but there are a few papers that discuss impaired leptin transport across the blood brain barrier.  A review paper [8] mentions the following things decrease leptin transport
 
·         Ovariectomising mice
·         Aging
·         Overfeeding and underfeeding
·         Triglycerides
·         C-reactive protein (CRP)
 
Besides overfeeding and underfeeding, the two that are most modifiable are triglycerides and CRP, which doesn’t change much because inflammation and MD/ER stress are largely responsible for elevated C-reactive protein and triglycerides, and the major mechanisms of leptin resistance (SOCS3 and PTP1B).  Elevated triglycerides are a result of insulin resistance and
 
* Adrenaline, insulin and glucose increase leptin transport

Sunday, April 1, 2012

Leptin Resistance

Hormone resistance can occur when the number of functional receptors is decreased or when the hormone has decreased signal transduction.  Suppressor of cytokine signalling 3 (SOCS3) and protein-tyrosine phosphatase 1B (PTP1B) inhibit the signal transduction of leptin, causing leptin resistance [1] [2] [3] [4] [5].  The next question becomes: what increases SOCS3 and PTP1B, and decreases the number of functional receptors? 

SOCS3

Lipopolysaccharide is an endotoxin of gram-negative bacteria, is highly inflammatory and potently induces SOCS3 expression by elevating pro-inflammatory cytokines such as IL-6 [7] [8].  The body is mostly shielded from LPS by the intestinal barrier, but more of it can enter the blood stream if bacteria overpopulate the small intestine (small intestinal bacterial overgrowth), if immune system is weak or if there is intestinal permeability [9]. 

Evidence to support the role of LPS and SOCS3 in LR and obesity: 

  • DIO results in altered gut bacteria and intestinal permeability [10]
  • Mice without enzymes that detoxify LPS are more vulnerable to weight gain [10]
  • Mice lacking TLR4, which detects LPS and induces inflammation, were resistant to weight gain in DIO [10]
  • Germ free mice eat less and have a lower metabolic rate, but are overall resistant to DIO [10]
  • LPS infusion has a similar effect as DIO [10]
  • LPS is 2.7 times higher in DIO (but 10-50 times lower than sepsis) [11]
  • Mice without the SOCS3 gene are resistant to DIO [12]

Small intestine bacterial overgrowth (SIBO) can the result of consuming a significant amount of indigestible carbohydrates that can be rapidly fermented by bacteria.  These carbohydrates are known as FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides and polyols).  The polyols are the sugar alcohols, which are used as non-caloric sweeteners and smaller amounts are found in some fruits, particularly stone fruits and pears.  The monosaccharides and disaccharides refer to fructose/sucrose, found in fruits and added sugar, with fructose malabsorption* and galactose/lactose, found in milk, with lactose intolerance**.  The oligosaccharides refer to fructans, found mostly in wheat and also in some vegetables like onions, and galactans, found in legumes.  Both fructans and galactans are poorly absorbed.  Soluble fibre is fermentable, but doesn’t have the SIBO effect because the fermentation is much slower [13] [14] [15]. 

Several nutrients are need for proper immune function such as iron, zinc, copper and selenium and vitamins A, B6, B9, B12, C, D and E.  Inadequate intake of these nutrients could suppress immunity [16] [17].  Chronic inflammation [18], stress and drugs like cortisone suppress immune activity [9] 

Things that can increase intestinal permeability include: gluten [19], ethanol [20], a high intake of fructans [21], pro-inflammatory cytokines, glucocorticoids, oxidative stress, NSAIDs, psychological stress and acute infections [22] [23] 

* Fructose malabsorption is dose and concentration dependent.  The rate of fructose malabsorption at 25g is 40% and at 50g is 60-70%.  The rate of sorbitol malabsorption at 10g is 100% [24].  In studies where fructose is providing ~60% of the total calories are the researchers measuring the metabolic effects or digestive/microbiota effects of high fructose? 

** Most people of middle/northern European descent aren’t lactose intolerant, but most people of southern European/Asian/African descent are lactose intolerant [24] 

PTP1B

Many reviews on leptin resistance mention endoplasmic reticulum stress (ER stress) as something that also causes LR.  This is because ER stress increases the expression of PTP1B [25], and PTP1B has the effect on leptin resistance.  Mitochondrial dysfunction (MD) is strongly associated with and often leads to ER stress because the ER has a high need for ATP and because elevated ROS from the causes and effects of MD can lead to oxidative stress in the ER [26] [27]. 

More evidence to support the role of MD, ER stress and PTP1B in LR and obesity:

  • Mice without the PTP1B gene are resistant to DIO [6]
  • ER stress inhibitors restore leptin sensitivity in DIO and lower food intake and body weight of obese mice [2]
  • ER stress is increased in other tissues in leptin resistance and obesity [3]
  • People with obesity tend to have lower numbers of mitochondria and a slower, less efficient electron transport chain [28] 

See my post mitochondrial dysfunction on how it can be caused, other downstream effects and how to support mitochondrial function.

Also, oxidative stress from the causes and effects of mitochondrial dysfunction is another source of chronic inflammation and elevates pro-inflammatory cytokines [29], which may increase SOCS3 and leptin resistance. 

Neurodegeneration

DIO quickly elevates pro-inflammatory cytokines, such as IL-1, IL-6 and TNF-α, and IgG in the arcuate nucleus of the hypothalamus, but not the liver or adipocytes, before weight gain [30] [31].  TNF-α can signal apoptosis in the hypothalamus and DIO increases apoptosis of hypothalamic neurons [32].  Overtime the number of leptin receptors decrease leading to less leptin signalling and leptin resistance. 

Inflammation and MD/ER stress are the main promoters of apoptosis, so this doesn’t change the overall direction.  But this supports the idea of obesity being a chronic disease and can explain why formerly obese people struggle with weight loss even when they are doing everything right.  Reducing the SOCS3 and PTP1B signal is likely much easier than growing and integrating new neurons (neurogenesis)