Tuesday, September 13, 2016

Is a low fat diet the path to weight loss?

It is completely understandable how low fat diets came to be popular. Before we had the tools to really study diet in large populations, it made a lot of sense. After all, fat contains 9 calories per gram, compared to 4 calories per gram for protein and carbohydrate. It seems logical that limiting the most calorie dense food would help one to lose weight. Now that our research methods are more advanced, we have had the opportunity to study the efficacy of low fat diets. It turns out that they really don’t work so well over the long term.

In a summary of the research literature, replacing 10-15% of dietary fat with carbohydrate results in a modest weight loss of 2-9 lbs. over the short term (6 months). However, over the long term (1 or more years) this weight is regained and there is no association between percent of dietary fat and body weight (Reference 1).

Why is this the case? For two reasons actually:

1) Dietary fat promotes satiety. It helps you feel full. Most people get really hungry a few hours after eating a low fat meal, particularly if it is high in carbohydrate and low in protein.

2) Dietary fat helps to stabilize blood sugar. Swings in blood sugar common with low fat, high carbohydrate eating patterns result in a reactive hypoglycemia that drives down blood sugar and increases insulin levels. For most people, this will result in increased hunger and overeating. 

Incidentally, these hormonal changes in blood sugar and insulin levels may also promote fat storage independent of caloric intake.

The most convincing evidence that low fat diets do not result in long term weight loss has been indirectly conducted right here in America over the past few decades. Our percent of calories from fat has steadily dropped from 40% of calories to 34% in the last 30 or so years. Have we gotten thinner? Not at all, obesity rates have skyrocketed in this time period.

1) Willett WC. Dietary fat plays a major role in obesity: no. Obesity Reviews 2002; 3:59-68.

A completely new way of thinking about weight loss

The Study
The prevailing wisdom about how to lose weight is to decrease calories and increase physical activity. This theory was put to the test in a very interesting study. One hundred and fifty four adolescents and 75 college age women underwent a two week baseline measure of their resting metabolic rate, energy intake, and body composition. Researchers created a variable for each subject called energy flux, which was calculated by adding energy intake and energy expenditure for each person. Subjects were then followed for 2 years to see who gained or lost the most weight.

The subjects with low energy flux were more likely to gain weight, while the subjects with high energy flux were more likely to lose weight. In other words, eating more calories and exercising a lot reduced the risk of gaining weight, while eating fewer calories and exercising very little increased the risk of gaining weight. American Journal of Clinical Nutrition 2016; 103:1389-96.

Take Home Message
This is a fascinating study that tells us 2 two things:

1) Exercise is extremely important for long term weight maintenance, which most of us already know.

2) Cutting calories a lot may not facilitate long term weight loss. This is a relatively new concept. 

Our body fights back really hard when we cut calories. Very few people can keep weight off long term when they lose it solely by reducing energy intake. The researchers believed that the reason the low energy flux group gained weight was largely due to significant decreases in resting metabolic rate as a response to the lower calorie intake.

Although this is just one study and more research is needed, it is becoming clear that weight loss is much more than just calories in versus calories out. The human body has awesome defense mechanisms to keep its body fat at what it considers to be a safe level. We have much to learn about these mechanisms.

I tell my weight loss clients to cut their calories slightly, not severely, and to make cardio and strength training a very consistent habit.

What influences appetite more, cutting calories through dietary restriction or through exercise?

The Study
In this randomized trial, 10 young men completed 2 separate interventions that created a 25% deficit of their energy requirements. This was done first by reducing calories by 25%, and later by exercising 25% of their calories away. Appetite and energy intake were measured after each condition. The results were a bit surprising. Despite the deficit being 25% in both interventions, subjects were significantly more hungry and ate more calories after reducing their food intake. American Journal of Clinical Nutrition 2016; 103:1008-16.

Take Home Message
For most people, losing weight over the short term is not that difficult. Keeping it off is the real challenge. We evolved in times of famine, drought and food scarcity. Our body developed some very good defense mechanisms to help keep our body fat at a safe level, including lowering metabolic rate and increasing hunger when faced with weight loss.

This study provides evidence that reducing calories creates more of this fight back response than exercise. This makes sense to me. I have noticed for years that drastic caloric restriction and rapid weight loss almost always results in an equally rapid regain of lost weight. I have found that the quicker the weight comes off, the quicker it comes back on. A more slow and steady approach to weight loss is imperative. Reducing calories moderately, but consistently, is the key. A well organized exercise program is the other part of the equation.


Is Cancer Preventable?

Most of the major chronic diseases, like heart disease and type 2 diabetes, are easy to study. Since they occur often, cohort studies have enough power to provide very useful information. Since they have intermediate endpoints (HDL, LDL, triglycerides, insulin resistance, etc), more short term study designs like randomized trials have been extremely important. As research methods have become more advanced, we have learned a great deal about heart disease, type 2 diabetes and how to prevent them both.

Cancer is something of a different story. It is not just one disease but 100 different diseases. Lung cancer has a very different story than skin cancer when it comes to causes, prevention and effective treatments. This is true for most cancers. This is what makes cancer so very hard to study. Cohort studies generally won’t have enough cases of distinct cancers to perform meaningful analysis for decades, if ever. Randomized trials are not really effective because cancer takes years to develop and doesn’t have hard and fast identifiable intermediates to study. 

For these reasons, we don’t know nearly as much about preventing cancer as we do about most other diseases. Since cancer is the 2nd leading cause of death in the U.S., it is imperative to learn as much as we can about its prevention. In the last year or so, some very influential studies were published. I thought I would summarize this research for readers of my newsletter.

Tomasetti, et al.

This study was published a year and a half ago and was quite controversial (Reference 1). It proposes that the majority of cancers have nothing to do with genetics or lifestyle factors. They are simply a function of the number of times a tissue’s cells divide. The more divisions, the more likely a random act of mutation will occur.

The authors of this study theorize that one third of cancer risk is lifestyle or genetic and that two-thirds is simply the bad luck of random cell division. What this study is basically saying is that almost 70% of your risk of cancer has nothing to do with how you live your life.

Song, et al.

This was a very large study that combined both the Nurses’ Health Cohort with the Health Professional Follow-up Study (Reference 2). Over 135,000 men and women were included in this investigation. Subjects were considered to have a healthy lifestyle pattern if they met the following 4 criteria:

1) Nonsmoker.

2) Moderate alcohol consumption (≤1 drink per day for women, ≤2 drinks per day for men).

3) A BMI between 18.5 and 27.5.

4) Weekly aerobic exercise totaling 75 minutes/week of vigorous cardio or 150 minutes/week of moderate cardio.

Rates of death due to cancer were compared between those with a healthy lifestyle and those without a healthy lifestyle. The population attributable risk for the healthy lifestyle score was 48% of cancer deaths for women and 44% in men. What this means is that if everyone in the cohort adopted these 5 habits, roughly half of all cancer deaths would be prevented.

These 2 cohorts, made up of mostly doctors and nurses, are generally more healthy than the average American. When they extrapolated the score to the U.S. population as a whole, these 5 factors would prevent 59% of cancer deaths in women and 67% of cancers deaths in men.

This study shows that lifestyle is very important when it comes to reducing the risk of cancer mortality and contradicts the first study presented. Two other interesting notes: 1) This study did not include dietary variables and 2) Some of the factors were a little relaxed. For example, a BMI of 27 or less was considered a healthy range where a BMI or 25 would have been a bit more strict. Therefore, the results from this study may actually underestimate the protective effects of a healthy lifestyle.

Moore, et al.

In this large study, 12 separate cohorts were combined to investigate the association between self reported physical activity and incidence of 26 different types of cancer (Reference 3). When all of the cohorts were combined, there were 186,932 cancers reported. The combination of the sample size and number of cancers reported provided a very unique research opportunity.

High versus low levels of physical activity were associated with significantly lower risk of 13 different cancers, including: esophageal, liver, lung, kidney, gastric, endometrial, leukemia, myeloma, colon, head and neck, rectal, bladder and breast.

Three other types of cancer were borderline significant: gall bladder, small intestine and non-Hodgkin’s lymphoma.

There was actually a slight increase in melanoma among those more physically active, so be sure to use sunscreen if exercising outdoors.

Previously, physical activity was thought to reduce risk of just a handful of cancers. This study showed that it does a lot more to protect us than originally thought.

Cancer is difficult to study. There is a lot of inconsistency in the literature due to methodological issues. I would say that there is definitely an element of bad luck with cancer that you don’t see in other diseases. However, it appears that a large percentage of cancers are preventable.

Here is what I recommend:
#1 Don’t smoke.
#2 Maintain a healthy weight.
#3 Exercise regularly, every day even.
#4 Eat a healthy Mediterranean style diet, limiting red meat and processed meats.

These 4 areas are a very good place to start if you are trying to reduce your risk of not only cancer, but other major chronic disease as well.

1) Tomasetti, et al. Variation in cancer risk among tissues can be explained by the number of stem cell divisions. Science 2015; 347:79-81.

2) Song, et al. Preventable incidence and mortality of carcinoma associated with lifestyle factors among white adults in the United States. JAMA Oncology. doi:10.1001/jamaoncol.2016.0843.

3) Moore, et al. Association of leisure time physical activity with risk of 26 types of cancer in 1.44 million adults. JAMA Internal Medicine. doi:10.1001/jamainternmed.2016.1548.