What Can We Do About It?
Let’s look into our modern food choices…
Different food sources have varying effects on weight gain. Modern life has brought us many advantages but sometimes our affluence introduces negative elements into our lives. Meat consumption is one such consideration. Although the consumption of red meat has decreased somewhat over the last two decades, our total meat consumption has increased steadily from the turn of the century to the present (3). Meat is a food of high energy density and total meat consumption is associated with weight gain in both men and women. Study results hold true even after being adjusted for initial weight, physical activity, education level, smoking status and even total energy intake. This means that even at the same calorie intake, more meat intake translates into more weight gain (1,2,4). All types of meat are associated with gaining weight but chicken appears to be the worst offender (5). Studies on carbohydrates have found that consuming a low-carbohydrate diet (where the carbohydrate is providing less than 47% of calories to the diet) is associated with a greater likelihood of being overweight or obese. One study illustrated that the lowest risk for weight gain is achieved when eating between 47% and 64% of daily calories from carbohydrate (6). Likewise, amounts of more than 70% of daily calories from carbohydrates, now seen only in traditional societies such as those of the Blue Zones, result in extremely vigorous and long-lived people with healthily low BMIs (33).
The intricate interplay of macronutrients
Carbohydrates are being given a wide birth today in some circles. One reason for this is the belief by many people that excess carbohydrate ingestion increases glucose levels in the bloodstream which, in turn, creates the high insulin levels that trigger fat storage. This theory is part of the argument given for eating a low-carbohydrate diet. However, this interpretation is faulty because carbohydrates are not the only macronutrient that increases insulin levels. Both protein and fat also stimulate insulin release (11,12). The “Insulin Index of Foods” published in 1997 showed that red meat, pork, chicken and fish all produce substantial insulin secretion (11). Additionally, when high protein foods are eaten along with carbohydrates the resulting insulin spike is double that which would have resulted from the carbohydrates alone (29,30,31,37).
Though insulin does encourage fat storage, carbohydrates are the least likely food source to end up as stored fat. Carbohydrate foods are broken down during digestion into simple sugars – glucose is the major end-product along with smaller amounts of fructose and galactose. Our bodies are very resistant to turning carbohydrates into fat because almost every cell in the body is designed to acquire their immediate energy needs from glucose. A major exception to this is the heart which runs on a mix of glucose, free fatty acids and ketones (39). Glucose not used for immediate energy is stored in the form of glycogen for future use. Human beings have body glycogen stores in the liver and muscles of about 15 gm per kg of body weight so we can squirrel away around two pounds of glycogen before any excess carbohydrate needs to be turned into fat (34). Glycogen stores contain enough carbohydrates to fuel a body for a day or two of fasting at the most; after that stored fat will take over. The only time carbohydrates are turned into fat is when more calories are ingested than can be burned or stored. Even then, some of the extra carbohydrate calories will be burned off as heat through a process called facultative dietary thermogenesis (8,10). The remaining extra carbohydrates can be turned into fat by de novo lipogenesis, a very inefficient process, wasting about 30% of the calories consumed (7,9). De novo lipogenesis has not been shown to contribute significantly to fat gain in humans (40).
Proteins are metabolized differently than carbohydrates. There is no storage space in our bodies for excess protein. Proteins are usually broken down into amino acids and used to build new proteins with specific functions needed by the body. If there is a shortage of carbohydrates or fat available for energy purposes, proteins are easily converted to carbohydrate to be used as immediate fuel. They can also be converted to fat by the process of gluconeogenesis to be stored for future use. (13).
Fats are broken down into fatty acids that can travel through the bloodstream and provide fuel for cells. Any fatty acids not burned for energy are packaged into bundles called triglycerides (three fatty acids and a glycerol molecule) and stored in fat cells. Fat cells have unlimited capacity for fat storage. An average person has enough energy stored as body fat to live for weeks or even months without food. Obese individuals have survived fasting periods of up to one year.
When carbohydrates are scarce, most of our body processes are able to run on fats. Those that can’t include red blood cells, the kidney medulla, bone marrow and some types of muscle fibers. These organs must still have a source of glucose to function properly (38). Brain cells cannot utilize fatty acids directly. When carbohydrates, the brain’s preferred fuel source, are low, the body is able to produce fat-like molecules called ketone bodies which brain cells can use for energy. It is thought likely that ketones exist primarily to provide a fat-derived fuel for the brain during periods when carbohydrates are unavailable (39). Along with ketone bodies, the brain still has the need for some glucose which can be produced by the liver and kidneys using protein from muscles and other body sources. In this situation, if the diet contains enough protein, muscles and other body structures will not be jeopardized (38).
How does all this translate into the best way to lose weight?
There is a great debate between proponents of low-carb diets and low-fat diets for losing weight. As discussed above, the insulin theory is not valid. Additionally, low-carb diets are high in animal protein which is associated with increased weight gain (1,2,4,14,15). Low-carb proponents state that eating a high protein/fat, low carbohydrate diet will induce the body to turn to fat for fuel. This is true, simply because there is no other fuel available. However, just as is the case when burning carbohydrates for body fuel, the fat being burned does not come out of body fat stores as long as the calories being consumed are close to or in excess of what you need. You burn what you eat.
Low-carb dieters site studies that imply that diets lower in fat have no advantage for weight loss. Regrettably, their data is based on so-called “low fat” diets containing 30% or more calories from fat. This is nowhere near genuinely low fat. Standard Western diets themselves average about 35% of calories from fat. No wonder these studies find no difference in weight loss. A true low-fat diet contains only about 15% calories from fat, although the fat level can vary from 10% to 20% depending on the exact mix of foods eaten. People who eat consistently at this lower level of fat are invariably found to be of healthily low body weight (35,36). This is the level of fat found naturally in a plant-based diet of whole vegetables, fruit, legumes, fruits and grains along with some nuts and seeds (32).
And on the subject of nuts…. the mystery of nuts and the disappearing calories…
Nuts are a good source of protein and healthy fats. They make a great snack except that they are calorie-rich, making people leery of eating them, especially if they are trying to lose weight. Surprisingly however, nuts do not seem to make people fat even when their addition to a diet adds a significant number of calories (16,17,18,19). Studies consistently show that the thinnest people eat the most nuts and the fattest people eat the least. Nut consumption is also associated with a lower body mass index (BMI) (20,21,22). In addition, a 2012 review of the literature showed that nut consumption improves lipid levels, reduces inflammation and improves arterial function, all without causing weight gain (23). In fact, every single study looking into the addition of nuts to a person’s diet showed that, even without restricting calories, the expected weight gain due to the added calories from nuts does not occur.
The answer to this mystery has only recently been explained. It turns out that nuts, including peanuts, enjoy some extraordinary attributes. First of all, nuts are so satisfying that they reduce the amount of other food eaten during the day (24,26). Secondly, because nuts require lots of chewing and some of their cell walls are difficult to break down, part of their calorie content travels through the digestive system intact. In other words, some of the oil never gets digested and leaves the body as waste (25,26). These two factors account for about 80% of the missing calories. What about the other 20%? Amazingly, eating nuts actually promotes the use of body fat stores. In other words, nuts boost metabolism by burning more stored body fat (25,27).
What wonderful news! You can enjoy eating nuts (in moderate amounts, of course) without worry about those extra calories.
The best diet for losing weight and maintaining a healthy weight for life is the same diet that prevents cardiovascular disease, cerebrovascular disease, diabetes, cancer and the many other diseases of affluence that are the main causes of death in our modern world. It should come as no surprise that this is a whole-food plant-based diet.
What if you still have trouble losing weight, even on a plant-based diet?
If you are eating a plant-based diet but seem to be having trouble losing weight, check the caloric density of your foods. Caloric density is the measure of how many calories are in a given weight of food. Eating a food low in caloric density provides you with much fewer calories than the same weight of a food high in caloric density. Because people tend to eat a similar weight of food every day, eating low caloric foods allows you to feel the same eating satisfaction while consuming fewer calories.
Caloric densities of plant foods vary widely. On average, try to keep your caloric density around 600 calories per pound of food eaten. This means you can eat liberally on fruits, vegetables, whole grains and legumes. Cut back on added oils, seeds, dried fruit and breads. Nuts can be eaten in moderation. (28)
Examples of caloric density of some foods;
Broccoli and other green leafy vegetables – 100 calories / pound
Fruit – 300 calories / pound
Whole grains and starchy vegetables – 500 calories / pound
Legumes – 600 calories / pound
Fats and oils – 4000 calories / pound
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