Your Urine is Not a Window to Your Body: pH Balancing – A Failed Hypothesis

pHOne of my first encounters with “alternative” health was the “pH balance” idea. A customer approached me at the pharmacy counter and asked for “pH test strips.” I asked him about kidney stones, diabetes – the usual reasons you test your urine. He told me he was healthy, and he was just monitoring his body’s “acid balance” and that he kept his body “alkali” to be healthy.  “You can’t change your body’s pH, sir – if your pH changes, you’ll die,” I explained, in my most reassuring pharmacist voice. “You don’t know what you’re talking about,” he snapped at me, “I adjust my pH all the time.” I handed over the urine testing strips, rang it into the cash register, and wondered, what is this guy talking about? Where did he get the idea he could manipulate his body’s acidity?

The pH balancing concept covers a variety of alternative health ideas, practices and treatments. The idea that our body’s acidity needs monitoring and adjusting is regularly promoted by “alternative” health providers – particularly naturopaths, but supported by pharmacies that sell urine test strips, and supplements like greens+ [PDF]. pH testing and monitoring is held out as a panacea for pretty much everything: “Virtually all degenerative diseases including cancer, heart disease, arthritis, osteoporosis, kidney and gall stones, and tooth decay are associated with excess acidity in the body” says a typical website.

The medical profession, and the medical literature, is quiet on the topic of pH balancing. So let’s consider a few questions. What’s the premise and hypothesis for pH balancing and testing our urine?  Does the amount of acidity in our urine give us meaningful insight into our health? Can dietary changes and and supplements prevent and reverse illness? Are health professionals overlooking a simple, effective tool to improve health, just to support the “industrial-pharmaceutical” complex?  Let’s take a closer look.

The Premise

Advocates of acid-base measurement argue that our diets have dramatic effects on our health, and that by measuring our urine, taking supplements, and changing our diet, we can avoid or eliminate most diseases. They way it’s described, when we eat “acid-forming” products like meats and cheese, our bodies turn “acidic” and illness results. To compensate for this acidity, we leach calcium from our bones. If we continue to maintain a diet high in protein and “acid forming” foods, our bodies will shed calcium and we can end up with osteoporosis, and other chronic diseases.  “Too much acidity in your system can cause everything from blemishes to back pain to diseases like breast cancer,” says the Shoppers Drug Mart magazine, Glow.  The solution to reducing acidity? Drinking alkaline water, cutting back on protein consumption, eating lots of fruits and vegetables, and taking supplements like Greens+ and coral calcium. Advocates call this an “alkaline” diet. And to measure whether we’re doing enough, we should test the acidity of our urine (or saliva) using pH test strips that tell us how much acid is being excreted. If, on balance, our urine isn’t acidic, then we’re doing things right. On an alkaline diet, according to proponents, we can lose weight, stop cancer, absorb vitamins, and have beautiful skin. Sounds incredible.

Let’s take a look at the science  behind the premise:

What is pH and acid balance? The pH scale is a measure of the acidity of a liquid. A pH of 7 is neutral. Anything lower is called acidic, anything higher is basic, or alkaline. The pH is a logarithmic scale – that is, a difference of 1 pH is a 10x difference.


Our blood’s pH is 7.4 – slightly alkaline or basic. Enzymes that facilitate chemical reactions in the cells work only in a narrow range of pH. Any significant change (below about 7 or over 7.7) means almost certain death. A series of buffers and compensation mechanisms keep the pH in our blood from moving far from 7.4. Because the blood circulates throughout the body constantly, it can compensate any changes in pH in any of our organs (e.g., our muscles during intense exercise). Carbon dioxide (CO2) is the most prevalent acid in our body, and is a product of cellular activity. The blood carries CO2 away and eliminates it in the lungs. The lungs actually provide the biggest source of acid elimination in our body.  Our kidneys provide a secondary protection of the pH, eliminating acid in the urine (but much more slowly than the lungs).

Consider the process of eating and digestion. Everything we eat is broken down by stomach acid. The pH in our stomach is about 3 – very acidic, due to production of hydrochloric acid. Everything that is ejected from our stomach, into our intestines, is then immediately neutralized by digestive liquids and enzymes. Everything we eat and digest will end up at the same pH in our intestines. What this means is the initial pH of any thing we eat is completely irrelevant. So let’s dispose of a few myths right away – alkaline water? kangan water? coral calcium? All without scientific merit. Even if you manage to raise the pH of your stomach significantly (say, with antacids), eventually the stomach acids will restore the stomach pH to its regular levels. Nothing you eat or drink will have a significant effect on the pH of food once it reaches your intestine to be absorbed.

What happens when this food is absorbed?

Organs and tissues that are perfused with blood share the bloods pH of approximately 7.4. This is because of a feature called homeostasis. All of the enzymes in our body function effectively only in a very narrow pH range – that’s why our body has several backups (lungs, blood buffers, kidneys) to keep our pH from changing much. So common alt-health statements like “cancer cells only thrive in an acidic environment and healthy cells do best in one that’s alkaline,” also from the Shoppers Drug Mart magazine Glow, are demonstrably incorrect. Leukemia and lymphoma, to name only two cancers, thrive in the blood at a pH of 7.4. And claims that “acidity is the root of all disease” are without basis – and reflects a lack of understanding of basic physiology and biochemistry.

But don’t bones leach calcium to neutralize all the food I eat? And doesn’t that lead to osteoporosis?

When our bodies metabolize foods, certain end products must be eliminated. These end products are sometimes called “ash”. End products may be acidic or alkaline. Meat is a source of protein, and diets high in protein tend to produce more acidic ash in the urine, due to some of the amino acid residues. (Meat actually has both “acidic” and “alkaline’ amino acids, and the process of digestion causes some “alkali” losses – so the net effect is “acidic” ash.) To neutralize the acidic ash in the bloodstream, there is some evidence that calcium can be resorbed from the bones  – and this is the basis of claims that diets rich in meat cause osteoporosis. But it’s not that simple. While some studies have shown that calcium loss increases with protein intake, the relationship appears to be complex. One of the largest and most recent studies, derived from the Framingham Heart Study, looked at the impact of diet on bone mineral density over a four year period. The consumption of magnesium, potassium, fruits and vegetables were associated with lower bone loss over four years. But protein, which the pH balance advocates claim will reduce bone mineral density, was also associated with less bone loss.[1] That is, higher consumption of protein protected bone strength. This effect has been shown in other studies. So it appears the acid-base theory isn’t as simple as advocates claim.

One of the authors of early and often-cited trial that looked at protein and calcium loss back in 1982 published a follow-up editorial to in 2001 to clarify the current evidence about protein consumption and bone loss:

” It is difficult to sustain a case, either evidential or deductive, for overall skeletal harm related either to protein intake or to animal protein. Indeed, the balance of evidence seems to indicate the opposite” [2]

Here’s another summary of the effects of food and calcium balance, also suggesting that the pH balance hypothesis may be inadequate:

“The adult human body contains about 1 kg Ca(calcium), and all but 1-2 % is contained in bone. In consequence, any factor that affects the amount of Ca retained by the body must alter total bone mineral mass. Nutrients that increase urinary Ca excretion, such as S-rich proteins, salt and caffeine, or that reduce net calcium absorption, such as fat, phytates and oxalates, are regarded as having a negative effect on bone. Conversely, nutrients that decrease calcium excretion, such as B, or increase calcium absorption, such as sugars and calcium, are regarded as beneficial. However, the situation is highly complex and the impact of these dietary constituents on long-term calcium balance and fracture risk is unclear. Some nutrients, phosphate for example, affect both net calcium absorption and excretion in such a way that there is little overall effect on calcium balance. In addition, some dietary components, such as fat and phosphate, are digested or absorbed in the small intestine at a faster rate than calcium, minimizing the potential negative effect on calcium absorbability. Where measurable effects on Ca balance are observed, the magnitude is often small and can be compensated for by small increases in Ca intake. Caffeine, for example, reduces calcium retention by increasing calcium excretion and decreasing calcium absorption, but the small effect, equivalent to approximately 3 mg calcium per cup of brewed coffee, is offset by the increased calcium intake associated with adding milk to the beverage. [Source]

The scientific evidence suggest the relationship between diet, “acidic ash” and and urine pH isn’t clear. High meat diets do not seem to affect calcium loss, which throws the entire hypothesis into question. The relationship of  “acid-forming” protein wastes with calcium loss is  not as as simplistic as is claimed. And while hip fractures seem (in general) to be correlated with cultures where high protein consumption (meat and dairy) seem to be high, direct evidence of harm of protein is lacking. [3].

What the research tells us is that the advice to strive for an “alkaline” body, is not supported by good evidence. There is no evidence to show that anything other than a healthy diet with substantial fruits and vegetables, adequate calcium and vitamin D, and normal amounts of protein, is necessary for bone health. And, not surprisingly, this is what the most respected clinical guidelines tell us:

Osteoporois Canada, in its clinical practice guidelines says the following about diet:

  • calcium and vitamin D, either as supplements or in diet are essential
  • magnesium supplements have no effect on the risk of hip fracture
  • consuming adequate amounts of protein is associated with a reduced risk of hip fracture

The Society of Obstetricians and Gynaecologists of Canada, in their guidelines [PDF], make no specific mention of dietary measures to improve or maintain bone health, beyond calcium and vitamin D.  I could find no reputable evidence-based clinical practice guidelines for diet that recommend much beyond calcium and vitamin D for the prevention or treatment of osteoporosis – because nothing else has been shown to consistently provide a benefit.

What does this mean to my urine, and the urine test strips?

Your urine’s pH varies, as it’s a waste facility for the metabolic waste. Excess acidity is eliminated in the kidneys. And this can be manipulated by your diet. Your urine’s pH will reflect a number of metabolic, digestive, and other processes. But measuring the urinary pH to estimate of the blood’s pH  is nonsensical, because your blood pH does not change unless you’re seriously, seriously, ill. There remains no convincing evidence to demonstrate that measuring (and manipulating) your urine’s pH has any correlation with your risk of medical conditions like osteoporosis or cancer, or any of the other medical conditions that advocate claim are the result of “excess acidity.”

What about osteoporosis? Does diet have any effect?

Yes. We know, with good evidence, that calcium and vitamin D intake are strongly correlated with a reduced risk of osteoporosis. That’s why it’s essential to maintain a diet rich in these products. With respect to fruits and vegetables, the evidence is less clear, but there seems to be a positive relationship between consumption and reduced osteoporosis risk. While we cannot conclude that one causes the other (correlation does not equal causation), there is no known downside to a diet rich in fruits and vegetables.

With respect to protein, as noted above, the effects are not clear. While it’s  promoted among pH balancing proponents that excessive protein consumption causes osteoporosis, the evidence isn’t clear. There is no reason to significantly reduce protein consumption in the hope of  reducing the risk of osteoporosis. In fact,the evidence suggests the opposite-consuming adequate protein seems to be important.

What about my “Greens” supplement? Doesn’t this help protect my bones and keep me alkaline?

The claim with the Greens “superfood” products like Greens+ Bone Builder:

Greens+ bone builder feeds the body the most alkalizing synergy of bone building nutrients including 3 forms of highly absorbable calcium, magnesium, vitamin D3 and lycopene. Benefits include reduced risk of osteoporosis and increased bone mineral density and promotes bone formation.”

Unfortunately, there’s no published evidence to demonstrate that Greens+ has any of these effects. If it provides a source of calcium and vitamin D, then that could be helpful. But the benefit is unrelated to pH balance or the acidity of your urine.

Interestingly, the Federal Trade Commission recently won a judgment of nearly USD$70 million against a manufacturer of coral calcium and another version of “greens”. The manufacturer of the greens product “Supreme Greens” made claims that the product was an effective treatment for cancer, heart disease, diabetes and arthritis. It also claimed that “Supreme Greens” caused significant weight loss, and could be taken safely by pregnant women, children and persons on medication. The court agreed [pdf] that the advertising for these products was deceptive.

What’s the bottom line with pH balancing and testing?

Urinary pH is highly variable, reflects the net result of your diet and any supplements you take. Following a “pH balanced” diet, and taking pH manipulative supplements has no demonstrated relationship to one’s risk of osteoporosis, cancer, or other serious illness. General dietary advice to consume plenty of fruits and vegetables, sufficient amounts of protein, vitamin D, and lots of calcium-rich foods is sound. Calcium and vitamin D supplements may be useful if you don’t get enough in your diet. But there is no evidence to suggest that your urine’s pH correlates with osteoporosis, or your risk for diseases like cancer. And there’s no need to take any special superfood or greens supplement to help protect or strengthen your bones, or to reduce your risk of cancer.

As summarized succinctly and accurately by Quackwatch,

“If you hear someone say that your body is too acidic and you should use their product to make it more alkaline, you would be wise not to believe anything else the person tells you.”


[1] Tucker KL, Hannan MT, Kiel DP. The acid-base hypothesis: diet and bone in the Framingham Osteoporosis Study. Eur J Nutr 2001;40:231-7.

[2]Heaney RP. Protein intake and bone health: the influence of belief systems on the conduct of
nutritional science. Am J Clin Nutr 2001; 73:5-6.

[3]Prentice A. Diet, nutrition, and the prevention of osteoporosis. Public Health Nutrition. 7(1A), 227-43.

For More Information

Acid/Alkaline Theory of Disease is Nonsense from Quackwatch

Busting Cancer Myths: Acidic Foods and Cancer Risks from

22 thoughts on “Your Urine is Not a Window to Your Body: pH Balancing – A Failed Hypothesis

  1. Pingback: uberVU - social comments

    • About 5 years ago I was suffering from adult onset asthma. An MD diagnosed the asthma and prescribed an inhaler. At the time I was testing my saliva acid level out of curiosity, and noticed that the asthma problem only happened on bad days when my fluids were testing acid (below 5.5). Interesting coincidence! I went on a three month diet eating at least two alkalizing meals each day (mostly meals of either apples or melon). At the end of this three month diet my fluids consistently tested around 7, and the asthma completely went away. I’ve not used the inhaler in the last 5 years. During these 5 years I’ve gained about 30 pounds and still test around 7 pH.

      I would suggest that although blood alkaline levels may be regulated by the body, the interstitial fluid alkaline levels may be less well regulated.

      I’d like to see scientific studies calculating level of correlation between acid level and various diseases (though a correlation does not necessarily prove cause and effect).

      Why is it that we spend so much effort monitoring the Ph of our swimming pool, but the medical establishment is so resistant to seriously studying any possible relationship between the Ph of our body fluids and the growth of the stuff our bodies are made of?

      • Steve – what makes you think the medical establishment doesn’t look at pH? I spent 23 years working in clinical biochemistry, and part of my job involved measuring arterial blood pH and sometimes urine pH. We understand very well the relationship between blood and other bodily fluid pH and disease. That includes saliva, which correlates very poorly with blood pH, and seems to be related to oral health, specifically the amount of bacteria living in the mouth. I wonder if your ‘alkaline diet’ was lower in refined carbohydrates which encourage bacterial growth in the mouth. That might explain your observations.

      • I also meant to mention that asthma might lead to a respiratory acidosis, because you are not efficiently exhaling carbon dioxide, which could explain the more acidic saliva on days when your asthma was worse. So the asthma might have been causing the acidic saliva, not the other way around.

  2. So would it be fair to say that the variance in urine pH based on diet is actually an indication of our body maintaining a constant pH, i.e.:

    pH levels in food
    – constant pH of body
    = pH we excrete

    Did I read this correctly?

    • Kind of. The vast majority of acidity in the body is from CO2 production, and it’s eliminated mainly by the lungs. There are also buffers in the blood’s plasma that can compensate for pH changes. So there are multiple channels for elimination. You could consider the urine’s pH as the end product of all the waste that gets eliminated there. Some is acidic, some is alkaline (basic). Some, but not all, of the wastes are the consequence of food consumption. The net amount of hydrogen (acidic) waste in any particular collection of urine is its pH.

  3. Pingback: Tweets that mention Your Urine is Not a Window to Your Body: pH Balancing – A Failed Hypothesis « Science-Based Pharmacy --

  4. Nice summary of the science.
    You folk must be overwhelmed with the crap coming out of alt-med websites these days!

  5. Thank you for posting this. I love your response to the customer asking for urine strips, you may not have changed his mind, but maybe someone else in the future will be swayed by your sound advice. Keep up the good work.

  6. I totally agree with you, but it is interesting how many cultures have the concept of “acid” being a source of unwellness.

    My own grandmother, from the North of England used to blame “acidity” for a lot of her health problems, when in fact she just had a really bad diet. She ate no virtually no fruit. Vegetables and meat were cooked to unappetising greyness. Her staples we porridge, bread and potatoes with lashings of animal fats. Then she wondered why she had indigestion and hypertension!

    The Chinese also have a concept of balancing acidity in foods. Apparently a health diet is three parts of yang to two parts of yin foods. There are also neutral foods.

  7. Pingback: Two more picks for your library « Science-Based Pharmacy

  8. Pingback: Skeptic at Work: The Alkaline Diet « skeptigirl

  9. Thanks for this, I have been waging a quiet battle against this sort of nonsense for a while now. I worked in a clinical biochemistry lab measuring blood pH and bicarbonate for several years and I can confirm that unless a person is very ill, their blood pH will be very close to 7.4.

    By the way, our bodies produce about 1 kg or 20,000 mmol of acids every day as carbon dioxide, a lot more if we exercise vigorously, and eliminate them effortlessly. A 4 ounce piece of beef generates about 8 mmol of acids, a liter of Coke contains 2.5 mmol of acids (pH 2.6 = 0.0025M). So the amount of acids generated in our diet is tiny compared to the amount our metabolism produces constantly. Experiments using ammonium chloride to induce a metabolic acidosis require
    4 mmol/kg
    and a low alkali diet to achieve this, or 15 mmol/kg and a high alkali diet. That means a 60 kg person would have to consume 240 mmol of acids daily, the equivalent of 7.5 pounds of beef or 96 liters of Coke each and every day to overwhelm their homeostatic mechanisms and produce acidosis.

  10. Thanks for your thoughtful article, but I have a few queries.
    Kreblozen talks of acidosis: but this is a a severe and life-threatening condition. Surely the acid–base hypothesis is based on the idea of a life-time’s worth of slowly losing calcium due to slightly increased acidity as the body attempts to reduce any ‘acid damage’ by releasing calcium from bone?
    Is it not possible that prolonged elevated processing of acidity does have physiological effects on the body?
    And, Scott, I agree there does seem to be much confusion and misinformation about this theory, but are you right when you say the stomach makes all acid, then the intestines change everything to being alkaline? What we eat is further broken down before it is absorbed. Proteins are further broken down in the intestines, as you know, and are then absorbed as polypeptides, etc. to be broken down later to amino acids in the body. And aren’t most of the amino acids we eat (i.e. in meat) acidic (e.g. glutamate) with lesser amounts of ‘alkaline amino acids?
    Also, too, isn’t the release of respiratory carbon dioxide a different issue, i.e. it’s carried by hemoglobin, not in the plasma, which is where most of the products from digestion are carried. It is blood/plasma that needs to be rapidly safeguarded from acidity: thus, the loss of e.g. calcium to buffer this process?

  11. Hi Susanna,

    I think the key to this is understanding how acid-base homeostasis works. The buffering systems in our bodies can cope with very large amounts of acidity without our blood becoming more acidic than it should be, and without calcium being lost from bones. This has been proved in several studies, including large scale studies of risk factors for osteoporosis, the effects of diet on bone turnover, and experimentally induced acidosis. Calcium loss does happen in mild chronic acidosis, which happens with some kidney disorders when the kidneys either cannot excrete acids or reabsorb bicarbonate, not uncommon in elderly people. In normal people this does not happen unless the usual acid-base equilibrium is upset, which requires a serious illness. There is not enough acid (or alkali) in any food to do this. This has been looked at very thoroughly. Despite the claims of some (including some nutritionists), who correctly point out that acidosis can cause bone loss, but fail to demonstrate acidosis in normal people, it is not true that normal people with normal kidney and lung function lose calcium due to “slightly increased acidity”. Slightly increased acidity simply does not occur in these people for any length of time. I can assure you of this having measured arterial blood pH in hundreds of people.

    If what you are suggesting was true, we would expect to see bone loss in people who tend towards more acidic blood and tissues. Athletes, and others who get a lot of exercise are often temporarily acidotic as a result of increased metabolism. This excess acidity (hugely more than in any foods, as I explained above) is easily excreted by the lungs and kidneys without calcium being leached from the bones – exercise actually reduces the incidence of osteoporosis. Diabetics may have episodes of acidosis when their blood glucose is to high, but again, there is no evidence of more bone loss in diabetics than in non-diabetics. The risk factors for bone loss are well known and do not include an acidic diet. In fact vegans (who tend to eat a very “alkaline” diet) are at a higher risk of osteoporosis than meat eaters, probably due to less calcium in their diet.

    The stomach is definitely the only place in the gastrointestinal tract that produces hydrochloric acid. It is pepsin in the stomach that requires acidic conditions to start breaking down proteins into smaller polypeptides. They are further broken down into amino acids by proteases and peptidases in the intestines. These enzymes work best in more alkaline conditions than pepsin. Human (and other animal) digestion is very well understood, and the ‘alternative’ versions promoted, without a shred of evidence that I have ever seen, by naturopaths like Robert Young completely contradict the observations and measurements of thousands of scientists over many years.

    The vast majority of the carbon dioxide in blood is transported from cells to the lungs dissolved in the plasma, not attached to haemoglobin. This dissolved carbon dioxide is an essential part of the bicarbonate buffering system that helps to maintain a constant blood pH.

    I hope this helps!

  12. The only reason to be checking the pH of your pee is to bee sure its between about 5.0 and 7.0 on the pH scale. If its more basic you could be leaving room for urinary tract infections. You have bacteria (natural body flora) that live in the lower portion of the urethra that help keep “bad” bacteria out. However, if you are stressing on the pH of your pee then you should really think about taking a Junior College human physiology class to get the basic idea of how the body works. There is always uric acid and urea in your pee, one obviously being an acid and the other is a base. There is also always a little bit of calcium in your urine, more if you happen to eat too much meat and dairy products but that has nothing to do with how acidic the food is.

    • Hi Ron,

      I am familiar with this study, which looks at the link between animal protein in the diet, bone density and risk of fracture in elderly women. I came across it while I was trying to find evidence that mild chronic metabolic acidosis is a common problem. Acidosis does occur in elderly people who have kidney problems, as a result of their kidneys not excreting hydrogen ions as efficiently as they might. There is a professor of urology (Lynda Frassetto) and a semi-retired doctor (Anthony Sebastian) who seem to believe the idea that we accumulate acidic wastes due to our modern unhealthy diet and develop a metabolic acidosis as a result, but they doesn’t seem to present any convincing evidence of this anywhere. All the studies I could find seem to show that metabolic acidosis in the elderly is simply a result of poor kidney function, not an accumulation of acid waste due to an acid diet (there is a strong positive correlation between glomerular filtration rate – a measure of kidney function – and bicarbonate concentration – a measure of acidosis). In other words, acidosis seems to be the result of ageing, not a cause. Maybe supplementing bicarbonate in elderly people might be a good idea (it can slow the decline in kidney function), but it might also be dangerous as they can’t excrete excess bicarbonate very efficiently.

      There are studies that show that giving potassium bicarbonate reduces calcium excretion and bone loss, but sodium bicarbonate does not have the same effect. For example Lemann J Jr, Gray RW, Pleuss JA. Potassium bicarbonate, but not sodium bicarbonate, reduces urinary calcium excretion and improves calcium balance in healthy men. Kidney Int 1989;35:688-695. That suggests it is the potassium that protects the bone, not alkalising. So it seems likely it is the potassium in a diet rich in fruit and vegetables that protects bones, not alkalinity.

      Though I read everywhere that it is the alkalising effects of fruit and vegetables that protect bone, several studies have found “that intakes of zinc, magnesium, potassium, fiber, and vitamin C are associated with higher bone mass in premenopausal women”. All of these occur abundantly in fruit and vegetables.

      So what happens if people eat a raw food diet rich in bicarbonates, a seriously alkaline diet? Less osteoporosis? No, more of it.

  13. Your conclusions are excellent. I would like to add two points. First, low urine pH might be better than high, because of its antibacterial effects and lower risk of calcium/oxalate stones. Second, excessive alkalisation may be dangerous as illustrated by milk/alkali syndrome.

  14. Pingback: Acid, Alkaline Diets, pH Balance And Cancer | Anaximperator blog

  15. Richard – you and Scott are both right, stomach acid has a pH of 1-2 when secreted, but as Scott wrote, “the pH in our stomach is about 3” as the acid mixes with food, drink, mucus, pepsin etc.

    I used to measure the pH of gastric aspirate back when gastric ulcers were believed to be caused by excess stomach acid, and were sometimes treated by cutting the vagus nerve. I would measure the gastric aspirate before, and after the vagotomy to be sure the operation was a “success”.

Comments are closed.