In the current obesity epidemic, more research must be done to help physicians determine which weight loss programs patients should follow â€” low carbs or fats?
Surprising as it may seem, scientists still do not know whether fats or carbs in a person''s diet contribute to weight gain.
And far more research needs to be done before physicians can better advise people which group of foods to cut out, said Dr. Ronald Krauss, director at Children''s Hospital Oakland Research Institute.
The outcomes of more studies have to be better tested so physicians can better understand which diets to recommend.
"A lot of science out there tells us how cells work, but when you look at outcomes — do people get diabetes or heart problems with certain kinds of diet — we lack outcome data â€¦ and therefore we are forced to make decisions and recommendations on the best science available," said Dr. Krauss, who is also a senior scientist in the Life Science Division of Lawrence Berkeley National Laboratory. "Many of us have been aware that the simple message of a low-fat diet is not based on the best science. We have increasing concerns that replacing carbs with fat is not the answer."
In a discussion on a recent NPR Science Friday program, both Krauss and Gary Taubs, author of "Good Calories, Bad Calories: Changing the Conventional Wisdom on Diet, Weight Control and Disease," and a contributing writer for Science magazine, debated whether fats contribute more to weight gain or whether carbs do. Both agreed more scientific data is needed to find the answer.
Both also agreed that obesity is the result of fat accumulation, that the amount of fat people store is controlled by insulin, and that carbohydrates drive insulin production. Obesity is also the result of excess fat accumulation, and fat is regulated by insulin.
Taubs said there was a need for a study that would at least illustrate whether reducing caloric consumption or limiting the amount of carbohydrates in a person''s diet is the better way to control weight gain. The current assumption is that if a person eats 500 more calories a day than required, those excess calories will be stored as fat. Taub''s carb assumption is that if a person eats 500 more calories a day — but lower amounts of carbs — a person will not get fat because low-carbohydrate diets will cause people to lose, not gain, weight — even if a person increases his intake by 500 more calories a day.
Foods high in dietary carbohydrates include sugar, starchy foods like potatoes and pasta and grain-based foods like breads and cereals. Carbohydrates can also be found in dairy products and fruits and vegetables, as well as many beverages.
The proposed study would give one group 3,000 calories a day and then keep track of the weight gain/loss during a six-month period. Another group would be put on 3,000 calories a day — but with a diet containing low or no carbs. In six months time, scientists might know whether calories or carbs cause weight gain. And such a study would run no more than $50,000, Taubs said. Such a study has not yet been funded, nor has it been done, he said.
Both Taubs and Krauss agreed that a low- or no-carb diet is reminiscent of the Atkins diet, but that scientific proof is needed to see if Atkins was correct in his low-carb assumptions.
The question, Taubs said, is what makes people fat. If carbs are the answer, then physicians could tell their patients to stay off carbohydrates. If fat is the answer, then low-fat diets can be prescribed to help patients lose the excess weight.
And scientists have long known that not all carbs are equal. Processed carbs (refined flours, sugars etc.) are worse than the carbs found in whole grains, fruits and vegetables.
To complicate things further, certain foods can cause a more dramatic blood glucose rise than others, even though they may have an equivalent amount of carbohydrates, gram-for-gram. This is attributable to the glycemic index (GI) or glycemic load (GL) of a food — those foods with a high GI will cause blood glucose to rise higher and faster than foods with a lower GI. Finally, it''s important to realize that reactions to all foods are highly individualized, and a meal that sends one person''s blood sugars sky high may barely cause a blip for another.
Carbohydrates also may contribute to LDL (low density lipoprotein) particles, Krauss said. LDL comes in different forms. "Simply measuring LDL doesn''t tell us about the type of particles. If you look at the smaller particles, they are elevated in overweight persons and in people who eat high-carb diets, particularly sugars," he said.
Large LDL particles are not dangerous, Krauss said, but smaller LDL particles are where carbs make a difference, and they could be the culprit for much of what happens," he added. "Our evidence is that saturated fat does not affect LDL, but carbs can affect it. Lowering cholesterol by lowering fat does not work."
When patients with heart disease are examined, their cholesterol levels are not any higher than others without heart disease, Krauss said.
Some societies are not obese, Taubs pointed out, but when non-obese people from, say, an Asian society switched to Western diets, they became obese. Scientists still are not sure exactly why, or why Western diets seem to add to weight gain, Scientists still don''t know, Taubs said, whether it''s the carbs in Western diets or the fats that make thin people from other cultures gain weight when they live on Western diets for a period of time.
"It is true that we are wired in complex ways genetically," Krauss said. "It is absolutely true there are huge amounts of differences. And most of us are wired to put on fat, although a few societies are not."
Both agreed that the answer to what specifically makes people fat has not yet been found.
—By Diana Diamond
Diana Diamond is the editor of the Healthcare Journal. You can reach her at firstname.lastname@example.org.