Metabolic mysteries: why some people can't lose weight even when they eat less
It's a familiar complaint: "I simply can't lose weight, no matter how little I eat."
As a nutritionist, I've worked with patients who fail to lose weight even when their food diaries show that they are being diligent about their diets. They assure me that they are accounting for every bite of food and correctly estimating portion sizes. They're convinced that a faulty metabolism makes it impossible for them to lose weight.
Yet a recent study suggests another possibility. In a 12-month weight maintenance study (other details of which are being discussed in this recent post), the subjects kept diet diaries, which were examined by the researchers at regular intervals. However, the researchers report that "it was apparent that, on average, women in both study groups had underestimated their food intake."
And not by a little bit. On average, the women reported having consumed 1370 calories per day. The researchers calculated that their actual calorie intake was 2044 calories per day. That discrepancy of 674 calories a day adds up to over 5 pounds a month!
The men, on the other hand, were spot on: They reported average intake of 1765 calories, the researchers estimated actual intake at 1771.
Anyone have any theories as to why women would be so much less accurate at recording what they eat, despite the fact that they traditionally do more of the cooking and food shopping and are presumably familiar with the weights and measures involved?
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Posted by: weight loss | Nov 19, 2009 5:34:17 AM
I think the weight loss factor totally depends on the person.So it depends on the nature of the internal structure of the body.
Posted by: brenda | Nov 17, 2009 12:48:25 PM
You may have heard recently on NPR about a new study (a mice study) indicating that beneficial gut bacteria and a diet low in processed foods and sugar were related to the mice being able to maintain a healthy body weight. Unforunately I can't recall it exactly, but something like this: sterile mice were inoculated with healthy human gut bacteria, one group was fed a diet of processed, high sugar pellets and the other fed whole foods pellets. Group #1 had significant changes in the strains of microflora and quickly gained wt, the other group easily maintained a healthy wt. Alternately, they fed mice with disturbed gut flora either the healthy or processed pellets and found that even a healthy diet was insufficient to positively affect the ecology of the gut and both groups of mice were unable to achieve a healthy weight. This study was big news (I think it as at Harvard...?) and is paving the way for greater future research. stay tuned! I'm saying "Finally!" science will begin to recognize the direct link between overall health, chronic disease, and the ecology of the gut.
Posted by: Pam | Nov 17, 2009 12:34:32 PM
Isn't anyone concerned about Pretty Polly's posting. Eating 900 or less calories a day for over a year except for days when she eats nothing - sounds a bit like an eating disorder to me.
As for the daily caloric intake issue, it doesn't take into account the muscle vs fat ratio or the amount of exercise impacting weight loss. It is my understanding that individuals who have a lower percentage of body fat have a higher resting metabolism rate.
Posted by: Colin | Nov 13, 2009 12:55:35 PM
@Kate: Monica left out the details of how the researchers calculated subject compliance. There were two methods by which the researchers estimated how much food the subjects were actually eating. The first was to look at their weight, BMI, etc. and calculate from that an estimated daily energy intake. Because the subjects were gaining weight, they had to be consuming at least that much.
But, you may argue, that assumes certain things about metabolism - and as several commenters here have argued, women's metabolism is not governed by strict laws of thermodynamics. So the researchers did something else. They asked subjects to provide urine samples from the days when they kept their food diaries. By measuring the amount of urea in the samples, they were able to estimate how much protein the subjects were consuming on those days - and for the women, it didn't match up. Women reported consuming less protein than they had to be consuming based on their excreted urea. So if they under-reported their protein, they must have been under-reporting their total energy intake.
Posted by: Hannah | Nov 7, 2009 11:46:36 AM
To Pretty Polly:
It's interesting how your comment illustrates the point the article was making, when you write: "...when I had a voluntary 40-day fast, eating nothing, except maybe a tiny piece of bread every four or five days." Fasting is to abstain from ALL food and drink that supplies energy (calories) to the body. If you were eating bread every few days, you did not do a 40-day fast as you are claiming you did.
That was the point of the discussion, how common is the practice of convincing yourself that you're eating less than you really are? Or even that you're fasting when you really aren't?
Posted by: Kate | Nov 4, 2009 3:19:38 PM
I don't mean to sound as angry as I probably do, by the way. But these results don't make any sense to me. If this is a study about weight maintenance, and the women were eating 2044 kcal and maintaining their weight -- which is a believable result -- how could the men possibly have been eating 1771 kcal and maintaining their weight? That would put the average man well into Calorie deficit.
Or is it in the weight loss portion of the diet that they're eating this many Calories? In that case, we should see a section where the women weren't losing weight and the men were.
The abstract doesn't report anything like that. So what really went on here?
Monica's Response: As usual, the abstract reports what the researchers focused on (or want you to focus on). To really get into the details, you have to read the whole article.
Posted by: Kate | Nov 4, 2009 2:33:26 PM
If they in fact responded similarly when all food was provided, then they're underreporting their intake. Without seeing the data, I don't know what 'responded similarly' really means, because I've seen some odd things classed as significantly similar or significantly different in studies.
Posted by: Sara | Nov 4, 2009 12:49:53 PM
I wholly agree with the tasting of food during cooking being an unaccounted-for source of calories. Also, sometimes it's a pain to measure everything, so it's easier to just guess - e.g., it's easy to count pretzels, but how about peanut butter? I was shocked at how many calories I was taking in once I started keeping track.
Posted by: Kate | Nov 4, 2009 11:56:40 AM
Unless there's a lot more to this than you've described, that's the least justifiable conclusion I've come across recently.
"I know a priori that the metabolisms of women and men behave exactly the same way under caloric restriction. So when I get a lot of data that tell me that they don't, obviously the data are flawed, and I should throw them out. I'll substitute this result as to what *must* have been happening from this theoretical calculation about an incalculably complex system instead.
"Indirect calorimetry? What for? Why do I need to *measure* the women's food intake or metabolic rates when I can simply decide that they're too stupid, or too dishonest, to accurately report their intake no matter how motivated they are?"
I doubt women can expect much help from an establishment so biased that it prefers to make up fictional data when the real data don't support their hypotheses.
Monica's Response: The researchers did have some evidence that the men and women responded similarly to calorie restriction because in the first phase of the study (when all food was provided) the men and women both lost similar amounts of weight. What's a more likely explanation: that the women's metabolic efficiency suddenly increased by 40% in phase 2 or that they were under-reporting their intake?
Posted by: Pretty Polly | Nov 4, 2009 10:56:50 AM
Based on my personal experience, all I can say is metabolism IS a mystery.
I need approximately 1400 calories to maintain my present weight.
For the past two years I have been ingesting an average of 900 calories a day - with many spells of 500 or less calories a day (for several days in a row).
There is no way I could have miscalculated my caloric intake because it wasn't a "diet" of my choosing; I ate what little was available, on a day-to-day basis.
(And often there was NOTHING available.)
And yet, after a spell of eating 500 calories a day AT MOST - while my physical activity was even INCREASED - I lost less than a kilo in ten days.
(The same happened years ago, when I had a voluntary 40-day fast, eating nothing, except maybe a tiny piece of bread every four or five days. And my physical activity was even greatly increased because after the third or fourth day of fasting there was a surge of incredible physical and mental energy, so I did a LOT around the house.)
I know that the metabolism seems to slow down when the food intake is drastically reduced. And I have inadvertently found my own proof: after days of not eating (or up to 500 calories - IF I was lucky) and not having lost even an ounce of weight, I ate a pizza (1000 + calories). The next day I ate another one. Two days later my pants were dancing loose around my hips and waist: it seemed I had lost at least a kilo at once.
(My digestion had not changed, BTW. It always was very slow, like my metabolism. I only go to the bathroom once, maybe twice a week - and yet I never feel constipated.)
But after that sudden drop the weight loss stopped again. I still ingest around 1000 calories or (quite often!) less a day, mostly quite healthy food (raw leeks, which I love, black beans, peppers, some cheese, a banana now and then - that sort of thing), but my weight doesn't seem to budge.
All in all, it seems the metabolism is such a personal mechanism that one should really only listen to one's own body. :)
Posted by: Chris | Nov 4, 2009 10:01:48 AM
@ Yvonne: While what you say is true, there are many instances where men are treated as the garbage can. Every time I'm at my mother-in-law's for dinner I wind up eating twice as much as planned simply because everybody else didn't finish their food.
Posted by: Alecu | Nov 4, 2009 9:23:23 AM
There are many people who eat healthy all their life, but without exercise, they don’t look so good. On the other hand, people who exercise but eat junk food look better, because, as Jack LaLanne (a TV Fitness pioneer ) says, exercise is the key. I have read on Project Weight Loss what are his tips for life's longevity. He never stopped teaching people about fitness and nutrition, not even now, going to 100. Jack LaLanne said “Everything you do in life, I don't care, good or bad--don't blame God, don't blame the devil, don't blame me, blame you. You control everything! The thoughts you think, the words you utter, the foods you eat, the exercise you do. Everything is controlled by you.”
Posted by: Patty | Nov 4, 2009 8:17:55 AM
Although this study is clearly flawed, it does a great job of illustrating the most important aspect of weight control - our psyche.
For whatever reason, it seems that women are more comfortable with lying to themselves, than men are. I see it with my own clients. Also, women seem a whole lot more concerned with what people will "think" of them if they report what they actually eat. Men don't seem to care as much.
I find diet diaries to be very unreliable tools, for most of my clients. In many cases it seems to create a lot of anxiety about eating, and guilt over poor choices (then the subsequent necessity to lie about it.) If I have a client do a diary, I tend not to ask to look at it. The need only to be accountable to themselves. Not me.
Posted by: Mariya | Nov 3, 2009 5:35:43 PM
Wow, that same thing must have been happening to me!
I only started using My Tracking three days ago and I found that instead of about 1100 calories I was consuming on three consecutive days ~ 1800, ~ 1700, ~ 1300 (today).
I think people/women underestimate the great difference one chocolate sweet, the occasional few nuts, a bisquit while visiting a friend,or that unaccounted for glass of milk or a small bunch of grapes actually make.
Been playing with My Tracking and finding out these absolutely surprising facts..
Thanks, nutritiondata.com!
Mariya
Posted by: yvonne | Nov 3, 2009 4:24:19 PM
Do you think some women "taste not waste" they taste their cooking, clean off kids' plates, clean the last bite of food out of the pan all in an attempt to not waste food. Men don't usually cook & clean. I know I do this. It's a terrible habit.
Posted by: Lesli | Nov 3, 2009 2:45:11 PM
Discrepancies can come from a host of factors. Did the women have dependents (both children and spouse)? Did they have jobs (full or part time)? If so, what industry? What were the exact instructions for the food diaries?
Not to mention the diary methodology:
...Dietary compliance was estimated by using 3-d food diaries. The subjects were instructed by a dietitian to provide as much information on food and drinks consumed (eg, brand name, volume, weight, and ingredients) over 3 consecutive days (2 weekdays and 1 weekend day). The food diaries and instructions for their use were provided at months 8 and 14 of the study. The subjects were asked to complete the diaries immediately before their scheduled visits at months 9 and 15...
Three days in two separate months just prior to their check-in visits. That seems highly flawed. I wouldn't trust statistics coming from SIX DAYS of a ONE YEAR study.
Additionally, 30 men completed food diaries vs. 20 women -- is that an acceptable margin?
Posted by: Becca | Nov 3, 2009 2:24:35 PM
How, precisely did researchers determine the discrepancy? Was it based on calorie counts that were inaccurate in the food journal? Or did they have access to a direct way of measuring what the subjects ate (as in, predetermining the quantity of foods that were to be eaten). Without a direct way of determining what each person was actually supposed to eat and comparing it to what they recorded eating, you can't adequately determine the accuracy of the diaries. The sort of bites, licks, and tastes that immediately came to mind as being part of the problem don't explain the discrepancy. If they weren't in the diary to begin with, then researchers have no way of knowing of their existence.
How do we know that men weren't underreporting how much they ate in their diaries? Was there a difference in the amount of weight loss that was maintained between men and women? According to the blog post, men had a more accurate estimate of caloric intake relative to the researcher's estimate than women did. I'd be extremely surprised if women maintained weight loss on a higher number of calories than what it took for men to maintain weight loss on. If women were indeed eating more calories than required for maintenance, they should have been less successful at maintaining weight loss (which is not indicated anywhere in the abstract, but is a possibility). More information as to how this caloric discrepancy was determined would be very helpful in deciding what it means.
Monica's Response: Good questions. The researchers estimated actual calorie intake based on the estimated metabolic requirements of the subjects and the change (or lack thereof) in their body weights. They were, in fact, eating the number of calories required for maintenance...around 2000/day. Had the women been eating as little as they reported (ca 1400/day), they would have been losing weight at the rate of about 5 pounds per month.
Posted by: Eugenia | Nov 3, 2009 1:09:23 PM
I think that women tend to eat while doing other things, like having a gab-fest, and eating at the same time. And when they're gossiping, they get blinders over the amount of food they're actually eating - even when evidence like a half-full carton of Ben & Jerry's turning into an *empty* carton stares them right in the face.
Also, I think the tasting that goes on while cooking gets underreported.
& maybe some women underestimate their self-control? I have some female friends who bypass the "open the bag of snacks, pour a little out into a container, & then put the big bag away" method, because they *swear* they can just have a little & be fine.
One of my best friends, who is one of those "I swear I don't over-eat" kind of people does things like this all the time. She'll complain to me about how she can't make time to exercise, so she *really* pays attention to what she eats. But when we'll get chips & dip, or ice cream, & I'll watch her blithely polish off a HUGE amount, & act like she just had a little bit. It seems like a huge amount of denial.
For the record, I find it really hard to talk to her about this, because I'm both blessed with a good metabolism & a small appetite. So I'm pretty thin, & it feels very...condescending to try to tell her what she's doing wrong. And she does *not* take it well.
