Are Plant- or Animal-Based Diets Better for Weight Loss?
Does the diet everyone is talking about really work?
Posted Feb 08, 2021
What is the best type of diet to go on to lose weight? The easy answer is, “whatever works.” Adherents of a diet plan because it worked will defend their way of eating to lose weight against any contenders. And many who are not sure will choose the one everyone is talking about, or the one advertised most successfully (remember the South Beach Diet?), the one with the most interesting packaged foods, the one your sister-in-law tells you about, or the diet on which some celebrity like Oprah Winfrey lost weight. When she lost 67 pounds on a liquid diet, and Optifast announced this on one of her television shows, it seemed like everyone who had to lose weight went on the same program. And, like Oprah, gained back the weight they lost once they went back to eating food.
For the past several years, the Keto diet has been promoted as the most effective and healthy way of losing weight, at least as understood by its proponents. Its selling points have been the severely reduced amount of carbohydrate allowed, perhaps an additional benefit for anyone who doesn’t like vegetables. The reduction in carbohydrate consumption is supposed to prevent a rise in insulin levels that normally occurs after carbohydrate is consumed. Insulin is looked upon as a hormonal culprit pushing sugar, aka glucose, the final product of carbohydrate digestion, into the cells. An article on the internet site Livestrong, explains that, “… eating too many carbohydrates can make you gain weight by disrupting your glucose and insulin levels and promoting fat storage.” How many is "too many" is not explained: Is it one serving of oatmeal, a cup of rice, a sweet potato, a bag of potato chips, or a quart of ice cream?
Low-carbohydrate diets are supposed to enhance weight loss because the high intake of protein and fat supposedly increases satiety, so the dieter is not likely to overeat. Moreover, if insulin secretion is prevented, the fluctuations in blood sugar levels that might lead to hunger are eliminated, according to a recent book published by the National Institutes of Health (NIH). The author also cites studies suggesting that people on a high protein-fat diet may use up to 200 to 300 more calories a day due to increased metabolic output than when they are on a high-carbohydrate diet.
There doesn’t seem to be a good way of ending the debate. Obviously, if someone is successful with one dietary approach, why change? But for those who are undecided, a recently published study might help with the decision.
Dr. Kevin Hall and his colleagues at the National Institute of Diabetes and Digestive and Kidney Diseases carried out a four-week study that measured calorie intake and weight change among individuals who were overweight but not obese. The volunteers were housed in the NIH in-patient research facility and given access to foods that represented a plant-based, high-carbohydrate diet, and an animal-based, high-protein-fat diet. They followed each food plan for two weeks in a random order. Care was taken to make sure the subjects did not know that the research was related to diets and weight. They were told to eat as much or as little as they liked. The researchers wanted to learn whether consuming a high-carbohydrate diet would, as predicted by the low-carbohydrate camp, lead to an excess of calorie intake and fat accumulation due to insulin secretion. Both diets contained the same amount of fat; the carbohydrate and protein components were varied.
The researchers found that when the subjects were eating the low-fat diet, they consumed about 550 to 700 fewer calories a day than when they were on the low-carbohydrate Keto diet. Both groups lost some weight, about two to four pounds, but a significant amount of fat was lost only with the low-fat diet. And the two different food plans had no effect on hunger before meals, or fullness after the meals. This finding contradicts claims that eating a high-fat diet subdues hunger because insulin levels remain low, or a high-carbohydrate diet intensifies hunger.
This study showed that the supposed weight-gaining effects of insulin secretion associated with high carbohydrate intake had no effect on food intake, hunger, and weight gain. Given the nutritional importance of consuming foods containing substantial amounts of carbohydrate because of their nutrient and fiber contents, this is good news from a nutritional perspective. It is also good news because of the possible positive mood changes that occur when carbohydrates are consumed due to the increase of the mood-stabilizing brain chemical serotonin.
But this study will probably not alter the decision of many to follow a low-carbohydrate Keto diet. To begin with, eliminating carbohydrates almost immediately causes a two- to four-pound weight loss due to the decrease in water held by the body by stored carbohydrates. When carbohydrates are introduced back into the diet, the water returns and the scale registers weight gain. Moreover, eliminating carbohydrates does eliminate an entire category of enticing foods often turned to as a source of gustatory pleasure: cakes, cookies, chips, ice cream, pies, crackers, fresh bread, pasta, pizza, tacos, and French fries. These foods are high in calories and often eaten in excess, especially in times of stress, boredom, anxiety, or even celebratory occasions. Saying no to all carbohydrates means never saying yes to a piece of birthday cake, even on your own birthday.
Thus, it is understandable that those who have made peace with eating only trivial amounts of carbohydrate will not want to revert back to their pre-Keto diet way of eating. But for those who are still deciding how best to lose weight, the results of the Hall study should help.