by Marion Nestle

Currently browsing posts about: Diets

Jun 27 2012

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.

The problem

  • 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.

The methods

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
Weight-loss 45 30 25  Not reported
Low-fat (high-carb) 60 20 20 ~400
Low-Glycemic Index 40 40 20 ~300
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 results

  • 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.
May 3 2012

New and delightful books about food

Paul Kindstedt, Cheese and Culture: A History of Cheese and its Place in Western Civilization, Chelsea Green, 2012.
Kindstedt, a professor of food science at the University of Vermont and co-director of its Institute for Artisan Cheese, has organized his history by time period and region, from the Paleolithic origins of cheese to current attempts to regulate raw milk.  His material is well referenced and the book is full of facts and observations that will delight cheese lovers.

Seamus Mullen, Hero Food: How Cooking with Delicious Things Can Make Us Feel Better, Andrews McNeel, 2012.

I don’t usually blurb cookbooks but I couldn’t resist this one from Seamus  Mullen, the chef-owner of Tertulia in lower Manhattan.

This gorgeous book proves without a doubt the point I’ve been making for years: healthy food is delicious!  Take a look at what Seamus Mullen does with vegetables, fruit, grains and everything else he cooks.  I can’t wait to try his 10 Things to Do with Corn.  His food can’t guarantee health, but will surely make anyone happy!

Apr 24 2012

Nutritionist’s Notebook: Starting a healthy lifestyle early

On Tuesdays, I answer questions about nutrition in NYU’s student newspaper, the Washington Square News.  Today’s is about youthful immortality.

Question: Many students have expressed that, being so young, they can eat whatever they want and stay thin. What kind of implications does the type of food we eat have on our body weight? If a student is thin but eats bad foods, are there still detrimental effects? Additionally, at what age does what you eat tend to have the biggest effect on you?
Answer: It’s not only youth that keeps college students trim. It’s the lifestyle: running to classes, late nights studying or partying, irregular meals, eating on the run. Once students get past the hurdle of the “freshman 15” — the weight gain that comes from unlimited access to meal plans — most do not gain weight in college.

It’s what happens afterward that counts. Even the most interesting jobs can require long hours in front of a computer or chained to a desk. Eating out of boredom becomes routine and, once middle age hits, it’s all over. The metabolic rate drops with age, and you can’t eat the same way you used to without putting on pounds.

The college years are a great time to start behaving in ways that will promote lifetime health. If you smoke cigarettes, stop while you can. Don’t binge drink. Practice safe sex.

As for diet, eat your veggies. Whenever you can, eat real foods, shop at farmers’ markets and learn to cook. Cooking is a skill that will bring you — and your family and friends — great pleasure throughout life. If you cook, you will always have the most delicious and healthiest of diets at your fingertips.

You don’t know how? Try an Internet search for “free cooking lessons online.” Mark Bittman’s Minimalist videos, for example, make things simple with results that can be spectacular.

Do the best you can to eat well now, and think of it as easy life insurance.

Apr 17 2012

Do We Need Better Advice About Eating Well? I Vote Yes.

The New York Times asked me, among others, to contribute to its  Room for Debate blog on the question of whether anyone could possibly need to hear one more word about what constitutes a healthful diet.  Here’s my two-cents’ worth:

Better Information and Better Options

Of course Americans need more information about eating well. Otherwise we wouldn’t have an obesity problem. In my daily teaching and contact with the public, I hear endless confusion about what to eat.

People are bombarded with conflicting advice, much of it from sources with a vested interest in selling particular foods, supplements or diet plans. Nutrition studies tend to focus on single nutrients, making their results difficult to apply to real diets. No wonder people have a hard time knowing what or whom to believe.

This is too bad, really. The basic principles of healthy eating could not be easier to understand: eat plenty of vegetables and fruits, balance calorie intake with expenditure, and don’t eat too much junk food.

If such principles seem hard to follow, it is surely because of how they affect the food industry. Balancing calorie intake often means eating less, but doing so is bad for business. Food companies must do everything they can to sell more food, not less.

So they make foods available everywhere — even in drug, book and clothing stores — and in very large portions. Few people can resist eating tasty food when it’s right in front of them. Large portions alone explain rising rates of obesity: they encourage people to eat more calories but to underestimate what they have eaten.

Healthy eating requires a food environment that makes it easier for everyone to make better choices. It also requires a food system that makes it cheaper to buy fruits and vegetables than less healthful foods, so everyone can afford to eat healthfully. Fix the farm bill!

Mar 27 2012

Nutritionist’s Notebook: Importance of fiber

This semester I answer students questions about nutrition on Tuesdays in the student-run Washington Square News.  Today’s is about fiber.

Question: We tweeted and linked to the article you were cited in The New York Times on Tuesday, and you mentioned the importance of fiber in a diet. How much fiber is good to have in a daily diet, and what does it do for our bodies? What are good sources of fiber — cereal bars, granola bars? How much is too much fiber?

Answer: You, like most Americans, probably get less than half the fiber you need. You can fix that by eating more vegetables, fruits, nuts, beans, peas and whole grain breads and cereals. Fiber occurs only in plants.

Eating these foods at every meal will do wonders for your digestive system. They help protect you against obesity, heart disease, Type 2 diabetes and even some cancers.

Fiber refers to a bunch of plant carbohydrates that human enzymes cannot digest easily. These come in two types: insoluble and soluble. Insoluble fiber, the kind found in grains, almost completely resists digestion. It has no calories.

But soluble fiber from beans and other vegetables can be digested to some extent by bacteria in your colon. They produce a little energy you can use.

Research shows that people who eat plenty of vegetables, fruits and whole grains with both kinds of fiber develop less chronic disease. But these benefits do not show up in studies using fiber supplements.

This means you are better off eating vegetables than power bars. If you must eat those bars, choose the ones with fruits, nuts and whole grain — real foods — high up on the ingredient list. Watch out for misleading claims about “good source of fiber.”  Check the Nutrition Facts panels — 3 grams is minimal, 5 is better.

If you are not used to eating fruits, vegetable and grains, eating more of them may make you feel gassy. Gradually include more. Your digestive system will be happier, and you will be healthier.