Is a Calorie a Calorie?
By Malden Nesheim and Marion Nestle
Ever since the 19th century, nutritionists and the general public have accepted the “calorie” as the unit of choice for describing the energy content of food. Yet some scientists still debate whether all food calories are the same.
Do calories from a chocolate bar, for example, have the same effect on your waistline as the same number of calories from an orange? Putting it another way—and getting to a oft-invoked question in the debate—will you be more successful losing weight with calories from a low-fat diet than with the same number of calories from a low-carbohydrate diet? Or might the reverse be true? (As protein typically occurs in low amounts in foods—10 to 15 percent in the average diet—a low-fat diet is necessarily a high-carb diet, and vice versa.)
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The New York Times front page today has a report of a long-term study at NIH of severe calorie restriction in Rhesus monkeys. It found that calorie restriction did not extend the monkeys’ lifespan.
I’m not at all surprised. My co-author and I reviewed the literature on calorie restriction for a chapter in our book, Why Calories Count.
The new study makes news because it contradicts a study done in Wisconsin showing that severe calorie restriction extends life. Severe means 25% to 30% fewer calories per day that are needed to maintain normal body weight. I’d call this a starvation diet.
An editorial accompanying the report of the study in Nature attributes the difference between the results of this NIH trial and the Wisconsin study to a difference in dietary composition, suggesting that calories differ in their effects.
Not necessarily. The Wisconsin study allowed the control monkeys to eat a lot of junk food and they were fatter than normal. The NIH study restricted calorie intake in its control monkeys so they maintained normal weight and were healthier. This is the simplest explanation of the difference.
Studies in rats, mice, and many other animals show that calorie restriction extends life.
But what about primates?
Starvation can hardly be good for health. It causes weight loss, of course, but also a host of physiological and psychological problems. These were extensively documented in humans during World War II in Ancel Keys’ Starvation studies.
The relationship between BMI and human longevity has been examined in several recent studies, all of which show similar results: Longevity is best associated with BMIs in the range considered normal or slightly overweight. Above that range—but also below it—mortality increases.
Being underweight is associated with higher mortality.
A Canadian study provides this example:
And one from the National Cancer Institute provides another:
The bottom line? Eat a healthy diet and balance calories to maintain a healthy weight within that range.
Here’s my once a month on the first Sunday Food Matters column for the San Francisco Chronicle, out today:
Nutrition and public policy expert Marion Nestle answers readers’ questions in this column written exclusively for The Chronicle. E-mail your questions to firstname.lastname@example.org, with “Marion Nestle” in the subject line.
Q: I’m confused about calories. If I cut calories to lose weight, does it matter what foods I eat? Or are all calories the same?
A: As the co-author of “Why Calories Count: From Science to Politics,” I hear this question all the time.
The short answer: Calories matter for weight. The choice of foods that provide the calories matters a lot for health and may make it easier for you to diet successfully.
To lose weight, reducing calorie intake below expenditure works every time.
To prove this point, a professor at Kansas State University lost 27 pounds in 10 weeks on the Twinkies diet – one Twinkies every three hours with occasional snacks of chips, sugary cereals and cookies. Even so, he cut his usual calorie intake by 800 a day. Anyone would lose weight doing that.
Only four dietary components provide calories: fat (9 per gram), carbohydrate and protein (4 per gram each) – and alcohol (7 per gram).
Does the particular mix of these components make any difference to weight loss? Yes, say proponents of diets low in carbohydrate, especially rapidly absorbable sugars and refined starches.
Low-carbohydrate diets are necessarily high in fat, and somewhat higher in protein. Do people lose weight on them because of the effects of carbohydrates on insulin levels or because low-carbohydrate diets help reduce calories?
This question does not have an easy answer, but not for lack of trying. Weight-loss studies are hard to do. Estimating calorie intake is notoriously inaccurate, and measuring calories is difficult and expensive.
The first measurement study I know of took place in 1964. Investigators from the Oakland Institute for Medical Research studied weight loss in five obese patients in a hospital metabolic ward. They calculated the number of calories needed to induce rapid weight loss in each patient, and fed each of them a liquid formula diet containing that number every day. Every few weeks, they changed the formula to vary the proportions of protein (ranging from 14 percent to 36 percent of calories), fat (12 percent to 83 percent), and carbohydrate (3 percent to 64 percent).
Regardless of the proportions, all patients lost weight at a constant rate. The investigators titled their study “Calories Do Count.”
This study was conducted under rigidly controlled conditions of hospitalization and involved actual measurements – not estimations – of calorie intake and body weight.
But what about weight-loss studies involving people who are not incarcerated? Since the early 2000s, numerous clinical trials have shown low-carbohydrate diets to produce greater weight loss than low-fat diets. Some also have observed improvements in blood pressure, blood glucose levels and blood lipids.
But it is so inaccurate to estimate calorie intake in such studies that most didn’t bother to try. This means they can’t say whether the weight loss was due to composition of the diet or to calorie reduction.
It’s possible that low-carbohydrate, high-fat diets make people less hungry, but the evidence for this is mixed. Most studies of extreme diets of any type report high dropout rates or failure to stick to the diet for more than six months or so. And even though initial weight loss is rapid on low-carbohydrate diets because of water loss, these diets are low in fiber and some vitamins.
One problem with losing weight is that it takes fewer calories to maintain smaller bodies. Dieting also reduces energy expenditure.
One recent study of that problem involved taking detailed measurements for several years, and illustrates the difficulties of obtaining definitive answers to questions about diet composition and energy balance.
The researchers wanted to know whether diet composition affected energy expenditure in very obese people who had just dieted off up to 15 percent of their weight. They found that a low-carbohydrate diet did not slow down energy expenditure nearly as much as a low-fat diet, meaning that low-carbohydrate diets might make it easier for people to maintain weight loss.
On this basis, the investigators said, “The results of our study challenge the notion that a calorie is a calorie from a metabolic perspective.”
Perhaps, but study subjects were fed prepared calorie-controlled diets for only four weeks, and lost and maintained weight under highly controlled conditions. Does diet composition matter for weight maintenance in the real world? Longer-term studies by other investigators show that diet composition makes little difference in the ability to maintain weight loss.
Most reviews of the subject conclude that any diet will lead to weight loss if it cuts calories sufficiently.
Obviously, some diets are better for health than others.
Face it. The greatest challenge in dieting is to figure out how to eat less – and to eat healthfully on a regular basis – in the midst of today’s “eat more” food environment. And that’s a much more important research problem than whether low-carbohydrate or low-fat diets work better for weight loss.
Now that the Supreme Court says that the Affordable Care Act is constitutional, it’s time to get those pesky menu labeling regulations in place. That Act, you may recall, included a provision to take menu labeling national.
The American Pizza Community (TAPC) represents chains like Domino’s Pizza, Papa John’s Pizza, Little Caesar Enterprises, the International Pizza Hut Franchise Holders Association, Hungry Howie’s and Godfather’s Pizza.
TAPC members want alternatives for menu labeling that “would work for pizza.”
When there are 34 million ways to top a pizza just at Domino’s, it’s easy to understand how the one-size-fits-all situation currently proposed doesn’t work for pizza.
On June 4, Food Chemical News said the pizza industry would be asking Congress for an exemption from the menu labeling final rule.
Two days later, TAPC denied that charge.
On June 19, the Washington Post reported that TAPC met with congressional representatives to push for changes to the menu labeling plan. What kind of changes? Could they include exemptions? Not clear.
TAPC is getting somewhere. Congressman John Carter (R-TX) has just introduced a bill to weaken the national menu labeling law. This would exempt supermarkets and convenience stores from having to post calorie information on prepared foods, gives a break to pizza, and allows calories to be listed by serving size.
Also in the meantime, Food Chemical News says the House Appropriations subcommittee told the FDA to narrow the focus of its menu labeling rule. Translation: leave out movie theaters and, maybe, pizza.
I happen to love pizza, but it is unquestionably a major source of calories in American diets. A slice of a big thick pizza can easily run 1000 calories. I’d like to think that some pizza eaters might find that information useful.
I think pizza places should label calories—really, they can figure out how to do it—and that’s what I told CBS TV on June 20.
Margo Wootan at Center for Science in the Public Interest (CSPI) has an op-ed in The Hill with a good summary of the reasons why menu labeling needs to get moving. If you agree, CSPI has a model letter you can quickly send to the President, the Secretary of Health and Human Services (the FDA’s parent agency), and the FDA.
What’s holding up the regs? First, the Supreme Court, but that’s no longer an excuse. The upcoming election maybe? That’s no excuse either.
USDA has just released the latest figures on nutrient intakes among Americans. These amounts are reported by a statistically determined sample of people interviewed as part of the What We Eat in America NHANES—the National Health and Nutrition Examination Survey.
Having just published Why Calories Count: From Science to Politics, I’m interested in calories.
The survey results from 2009-2010 for calories per day for adults over the age of 20:
- Men 2512
- Women 1778
How many of those calories are consumed away from home?
- Men 35%
- Women 30%
How are daily calories distributed?
No, the percentages do not add up to 100%. That’s because of snacks. What percent of calories is consumed as snacks?
- Men 24%
- Women 23%
No surprises here, but the figures are fun to play with.
Compared to the figures reported in Why Calories Count for 2008, the figures for daily intake are not significantly changed.
Note: These are reported figures, and remain well below the 3000 calories a day for men and 2400 for women observed in studies that actually measure calorie balance.
Does where calories come from matter to weight maintenance? A new study says yes, but I’m skeptical.
As the co-author of a recent book called Why Calories Count: From Science to Politics, I am well aware of how difficult it is to lose weight.
- When you are dieting and losing weight, you require fewer calories to maintain and move your smaller body, and your metabolism and muscle activity—and, therefore, your total energy expenditure–slow down.
- To maintain the weight loss, you need to eat less than you did before you began dieting.
But what would happen if you could adjust your diet to keep your energy expenditure from slowing down?
Enter Ebbeling et al in JAMA, with a comprehensive study to address precisely that question. The results of the study and editorial comments on the findings demonstrate how complicated and difficult it is to obtain definitive answers to questions about diet composition and calorie balance.
- The investigators asked whether calorie-controlled diets containing varying amounts of carbohydrate, fat, and protein, and varying in glycemic load (a measure of rapidly absorbable carbohydrates in foods) affected total energy expenditure in obese people who had just lost 10% to 15% of their weight, but were still obese.
- They found that the diet lowest in carbohydrate did not slow down energy expenditure as much as did the low-glycemic index diet, or the one lowest in fat.
- They concluded: “The results of our study challenge the notion that a calorie is a calorie from a metabolic perspective.”
This study took years and involved a very large number of state-of-the-art physiological measurements.
But I want to focus on the question of whether calories from all sources are metabolically equivalent. Here’s my understanding of the study.
Ebbeling et al started by offering $2500 to obese volunteers to participate in a 7-month weight-loss trial. In my view, the 21 subjects who finished the study worked hard for that money.
They had to participate sequentially in a:
- Weight-monitoring phase for 4 weeks, during which they ate their typical diets while the investigators monitored their weight.
- Weight-loss phase for 12 weeks, during which they were fed pre-prepared diets calculated to contain about 60% of their usual calorie intake so they would lose about 2 pounds a week. The average weight loss over 12 weeks was an impressive 14.3 kg (31.5 pounds).
- Weight-stabilization phase for 4 weeks, during which they were fed pre-prepared diets that provided the reduced number of calories needed to maintain their newly reduced weights.
- Testing phase of 4 weeks on each of three pre-prepared test diets (total: 12 weeks). All three test diets provided the number of calories needed to maintain the reduced weight. During each of the 3 testing periods, investigators measured—not estimated—the subjects’ total daily energy expenditure (resting metabolism plus activity).
The composition of the diets
|DIETS||CARB%||FAT%||PROTEIN%||DECREASE IN TOTAL ENERGY EXPENDITURE, Calories/Day|
|Very low carb (high-fat)||10||60||30||~100|
Note that whenever one component of a diet gets changed, the other two components change too. Because protein usually occurs in foods in relatively low amounts, a low-fat diet is necessarily a high-carbohydrate diet, and vice versa.
- The weight-loss part of this study showed that when overweight people were allowed to eat only calorie-controlled pre-prepared diets, they lost weight quickly and maintained the weight loss.
- The test-diet part of the study showed that the diet lowest in carbohydrate (and, therefore, highest in fat) had the least effect in slowing down total energy expenditure. The diet that slowed down overall energy expenditure the most was the one lowest in fat.
If these results are correct, people eating high-fat, low-carbohydrate diets are likely to have the easiest time maintaining weight loss. In contrast, people on low-fat, high-carbohydrate diets are likely to have a harder time maintaining weight loss.
But does this mean that calories from different sources have different effects on metabolism? Proponents of the Atkins (high-fat, low carb) diet say yes, according to an account in USA Today (in which I am also quoted).
I’m still skeptical. The subjects in this study lost and maintained weight under highly controlled, calorie-restricted conditions, in which the calories came from a relatively low-fat, moderate-carbohydrate, high-protein diet (average diets contain 10% to 15% protein).
The accompanying editorial notes that heat losses are greater for protein than for carbohydrate or fat, and also raises questions about whether physical activity declined more with the low-fat (high-carb) diet than the others. It also notes:
Each diet was consumed for only 4 weeks. A weight stabilization protocol…may not have adequately accounted for changing energy needs associated with readjustment to new diets.
These provocative results…emphasize the current incomplete knowledge base regarding the importance of dietary macronutrients and energy expenditure, especially after weight loss.
Under the relatively short, highly controlled feeding conditions of this study, the composition of the diet may indeed matter to metabolism. But does diet composition matter for weight maintenance in the real world?
Other longer term studies of “free-living” people out and about in their communities show little difference in weight loss or maintenance between one kind of diet and another.
More research needed!
The bottom line
- If you want to lose weight, eat less (it worked well for the subjects in this study).
- It may help to avoid excessive consumption of sugars and easily absorbed carbohydrates.
- Once you’ve lost weight, adjust your calorie intake to maintain the weight loss.
- And understand that science has no easy answers to the weight-loss problem.
Ordinarily I find government plans of this type to be soporific but this one is especially well written and well thought out (with some caveats).
The report is a statement of FDA commitment to what it is going to do in the next four years in food areas that affect people and animals. It includes many promises, among them this one of particular interest:
Program Goal 4: Provide accurate and useful information so consumers can choose a healthier diet and reduce the risk of chronic disease and obesity
Objective 1. Update the Nutrition Facts label.
- Publish proposed rules updating the nutrition facts label and serving sizes [OK, but by when?].
- Publish final rules updating the nutrition facts label and serving sizes [Ditto].
Objective 2. Implement menu and vending machine labeling regulations.
- Publish final menu and vending machine labeling regulations [OK, but by when?].
- Collaborate with states, localities and other partners to ensure high rates of compliance.
Objective 3. Improve consumer access to and use of nutrition information.
- Explore front‐of‐pack nutrition labeling opportunities [Explore? See comment below].
- Collaborate with public/private sector parties on nutrition education [Collaborate? See comment below].
- Implement updated standards for the labeling of pet food including nutrition and ingredient information [How about a Pet Facts label for pet foods that someone might actually be able to understand?].
- Implement standards for animal feed ingredients.
- Publish final rule defining and permitting use of the term “gluten free” in the labeling of foods.
Goal-setting processes usually include dates by which the objectives are to be completed. These do not, which suggests that the FDA can continue to delay action until 2016.
I also do not understand what is meant by “Explore front‐of‐pack nutrition labeling opportunities.” Explore? The FDA has already sponsored two Institute of Medicine reports on front-of-pack labeling. Does this mean the agency is ignoring them and intends further research?
And “Collaborate with public/private sector parties on nutrition education?” What does the FDA have in mind for the content of such education? You can bet that no collaborative campaign can focus on “don’t drink your calories.”
FDA needs to deliver on these items, and sooner rather than later. This year? I’m not counting on it.
My Tuesday question from student readers of NYU’s Washington Square News:
Question: How can we determine our individual caloric, vitamin, carbohydrates, fats and other intake requirements per day based on our own individual weight, height and lifestyle?
Answer: You can’t. You will have to be satisfied with estimates based on measurements performed years ago on a small number of study subjects.
We require calories and nutrients — 40 to 50 separate substances that our bodies cannot make, we must get from food. Because these interact, studying one at a time gives results that may well be misleading.
Early nutrition scientists got “volunteers”— in quotes because study subjects often were prisoners — to consume diets depleted in vitamin C, for example. They waited until the subjects began to develop scurvy, a sign of vitamin C deficiency. Then they fed the subjects the smallest amount of vitamin C that would eliminate symptoms.
Because individuals vary in nutrient requirements, scientists used this data to estimate the range of nutrient intake that would meet the needs of practically everyone.
The Institute of Medicine compiles such data into Dietary Reference Intakes and presents the estimates by sex and age group. You can look up your requirements in DRI tables. DRIs account for the needs of 98 percent of the population. If your requirements are average, you will need less.
Few American adults show signs of nutrient deficiencies, but if you are worried about your own intake of nutrients, you can take a multivitamin supplement. Note, however, that we have no evidence to show supplements make healthy people healthier.
You can estimate calories by looking up everything you eat or drink in food composition tables, but it is easier to weigh yourself at regular intervals. If you are gaining weight, you are eating too many calories for your activity level.
With nutrition, it’s best to get comfortable with estimates and probabilities.
Fortunately, eating a healthy diet takes care of nutrients without your having to give them a thought. Eat your veggies!
A version of this article appeared in the Tuesday, May 1 print edition. Marion Nestle is a contributing columnist. Email her questions at email@example.com.