Diet, exercise & calories.

At its most basic level, weight gain occurs when calorie intake exceeds calories expended. The reverse is true about weight loss. This math, however, changes in predictable ways when the brain detects fat loss — appetite increases and metabolic rate decreases to favour weight regain.

What if there were clearly no best diet for weight loss? What if exercise alone were generally ineffective at promoting significant weight loss? Could you consider finding your own "best" diet and your "best" exercise level — with best defined as the healthiest you can maintain that is still enjoyable?

Calorie deficit

At its most basic level, weight gain occurs when calorie intake exceeds calories expended. Conversely, weight loss only occurs when energy intake is less than total calories burned. Weight loss occurs when calorie intake is reduced — regardless of the percentages of fat, protein, or carbohydrates eaten. Calorie intake, not carbohydrate intake, is the determinant of body fat gain or loss.

At this point, the calorie content of food is literally the only food property that has ever been convincingly demonstrated to impact how much fat is carried in our bodies. This was most recently validated by a meta-analysis1 of 20 studies suggesting that, for all practical purposes, a calorie is a calorie as it relates to body-fat-weight.

Studies2 consistently show that, once heavier, heavier individuals consume and expend approximately 20–30% more calories than lighter individuals. Studies held within tightly controlled laboratories and dormitories demonstrate that reducing calorie intake by this same number invariably causes fat losses, suggesting that higher calorie intake is required to maintain higher weights.

Weight loss happens only if calorie intake is lower than the total number of calories we burn — but the math should not be mistaken as simply "calories in, calories out." The math changes in predictable ways when the brain detects fat loss (the GateKeeper) and generates increased appetite and decreased metabolic rate to favour weight regain.

Diet

What is the best diet for weight loss? What if the answer were a resounding none?

You will be asked to consider disregarding the debate about the optimal weight loss diet. Despite years of searching, no best diet has been found. Countless studies comparing different diets — low-carbohydrate, ketogenic, low-fat, intermittent fasting, Mediterranean — have shown minimal and inconsistent differences in weight loss and health outcomes. In randomized controlled trials, low-carbohydrate and low-fat diets yield similar and very modest long-term weight loss results; weight loss differences between the two diets are minimal after 12 months.

The generally invalidated carbohydrate-insulin hypothesis

"I thought carbohydrates were bad for you?"

There is a decades-old popular hypothesis that says your weight is about the carbohydrates you eat, not the calories. This hypothesis says that when you eat sugar and simple carbohydrates, your insulin levels increase — resulting in the storage of fat, increased appetite, and slowed metabolic rate. This is the Carbohydrate-Insulin Hypothesis (CIH), and it is the theoretical basis for all low-carb dieting, ketogenic dieting, and intermittent fasting.

But is it true? Fortunately, hypotheses can be tested. Is insulin the determining factor in fat gain due to its direct effect on fat cells, hunger, and metabolic rate? The majority of evidence is contrary to the CIH.

In 2012, millions of dollars were raised and the Nutrition Science Initiative (NuSI) was founded to investigate the carbohydrate-insulin hypothesis. The organizers were proponents of low-carb dieting and they set out to prove the hypothesis. They organized three significant clinical trials and recruited three serious researchers: Kevin Hall, Christopher Gardner, and David Ludwig. Of the three published studies funded by NuSI, at least two — and possibly all three — decisively refuted the carbohydrate-insulin hypothesis.

Taken together, it has been a tough few years for the science of low-carb dieting and the carbohydrate-insulin hypothesis.

What about intermittent fasting?

Ethan Weiss, a cardiologist at UCSF, was successful losing weight using intermittent fasting — but he was uncomfortable recommending it to his patients because of a lack of research with human subjects. He decided to conduct the first-ever human randomized controlled trial comparing intermittent fasting with continuous eating. The researchers chose a 12 PM–8 PM eating window. The primary endpoint was weight loss at 12 weeks.

Adherence is the key, not diet.

Across all of these trials, look at the individuals in each waterfall plot who lost the most weight. They are the participants who best maintained adherence to the behavioural changes — primarily, to eating less. The only consistent finding among trials that compare diets is that adherence — the degree to which participants maintained effort and continued in the program — was strongly associated with weight loss and improved health.

Can you find help with adherence? It is the fundamental role of a weight management behavioural program to support and improve adherence. Behavioural programs lead to greater success because they support adherence. The eight modules in this material comprise a comprehensive behavioural program.

Eating healthily

Eating healthily promotes the health of body and mind. There is minimal controversy as to what constitutes eating healthily: minimally-processed whole grains, fruits, vegetables, lean proteins, lean dairy, good fats, and minimal alcohol. At the same time, most of us value food and drink, fun and friends, socialization, celebration — and the unique role food and drink play in all of these experiences.

Would you consider finding your own "best" diet — the healthiest eating that is realistic, enjoyable, and sustainable? The behaviours and effort level adopted to lose weight will be the same behaviours and effort level needed to maintain weight loss. Consider eating in a pattern and at an effort level that is both enjoyable and sustainable.

In a parallel nutritional program, you will learn about the calorie density of foods and how to estimate portion sizes, so that you can make the best assessment of your calorie intake. You will be invited to consider tracking your intake — while being made aware that self-monitoring of food and drink intake is not for everyone.

Exercise

Next to quitting smoking, physical activity is the most valuable behaviour available to improve longevity, quality of life, and reduce the risk of chronic disease. You will be encouraged in this program to be active, to identify obstacles to physical activity, and to develop skills and strategies to overcome those obstacles.

Surprisingly, studies show that exercise alone will not promote significant weight loss in most people. An important systematic review and meta-analysis7 of randomized controlled trials found that moderate-intensity exercise programs of 6 to 12 months' duration were associated with only modest improvements in weight (~4 pounds), waist circumference (~2 cm), and cardiovascular risk in populations with overweight and obesity.

Why exercise is limited as a weight loss tool

Exercise, despite its significant health and quality of life benefits, may have significant limitations in its ability to establish a calorie deficit. In a landmark clinical trial, Herman Pontzer8 and colleagues showed that even low levels of physical activity increase the number of calories we burn — but at higher levels of activity, there is no expected rise in energy expenditure. The body adapts to maintain total energy expenditure within a narrow range. This is called the constrained model of energy expenditure.

What this model suggests is that if you were to burn 400 calories today on a treadmill, your body would, over time, burn 400 calories less than what it was going to anyway — to make up for the extra calories you burned. If this seems unfair, it may seem less unfair if you consider that this mechanism would have been adaptive in an environment where work was required to find food and calories could be scarce.

Why exercise is still essential

This information is critical to understanding the place of exercise in weight management — but it must be read alongside the rest of what exercise does for you.

You learned in the Modulators module that stress, fatigue, depressed mood, and anxiety can all challenge weight loss efforts by increasing your appetite and decreasing your ability to self-regulate against wanting. Exercise can be very beneficial because it clearly and positively impacts stress, fatigue, and mood. In fascinating trials9, exercise has been shown to potentially directly reduce wanting signals in the brain, dampening the GoGetter.

Like best diet, you will be asked to establish your best activity level — the highest level of activity that is enjoyable, reasonable, and sustainable.

Find your best diet. Find your best activity level. Define best as: the healthiest you can maintain that is still enjoyable.