What Does Eating Plants Do For Weight Loss? Part Three

Recent interesting discoveries around weight issues

Does exercise help with weight loss?

Exercise is without a doubt a healthy activity, not only for your physical body but also for your mental health. Exercise is known to lower the risk of many of our increasingly common diseases, including heart disease, diabetes, obesity, osteoporosis and some cancers (10,11,12,13,14,15). In fact, people who exercise regularly have up to a 50% lower risk of dying from many of these chronic illnesses (10). Exercise also has a positive impact on mood that is comparable to that of taking antidepressant medication (28,29). The effect of exercise on weight loss however seems to be actually quite small. The following are some of the many contributing factors.

The calorie level in our diets has increased. The level of physical activity in both North America and Europe has increased over the last few decades….right along with our average weight. Any beneficial effects this extra exercise might have produced have been buried under the excess energy in the food we are eating (24).

Exercising people tend to eat more. This could stem from the idea that, because a person is exercising, they can indulge in a bit of reward eating (19). Simple increased appetite from exercise has a hand in this too. The hormone ghrelin, dubbed the “hunger hormone”, has an important influence on energy metabolism and stimulates the appetite. Ghrelin level is decreased after intense exercise. Unfortunately, the appetite suppression is short-lived and returns to normal after only half an hour (20).

The calorie burning power of physical activity is often overestimated (23). For example, a 500 ml carbonated drink contains 210 calories, which would require a 7 km run or an hour of walking to make those extra calories disappear. Even if people understood the amount of exercise required to compensate for extra calories, most people in this hectic modern world would not have the time to do it (22).

It’s not that exercise doesn’t help at all. People who actually perform high levels of physical activity (at least 1 hour of intensive exercise every day) are more likely to lose weight and keep it off (25,26). And people who combine exercise with diet experience a slightly faster loss of weight along with improvements in blood lipids and blood pressure (21,22). Exercising also helps to maintain muscle that can disappear during weight loss. In turn this helps to keep up a higher metabolic rate, a helpful component for further weight loss (16,17).

It seems that much of the improvement exercise offers stems from factors other than weight loss itself – improvement of body composition, decrease in blood pressure and lipid levels and improved mood (18).

What about the “healthy obese”?

Over the past few years headlines have proclaimed that some people who are obese (have a BMI of 30 or more) show no signs of obesity related problems such as abnormal blood fats, poor blood sugar control or diabetes, and high blood pressure. New research disputes this theory. In a study of 3.5 million British citizens, the apparently metabolically healthy obese had twice the risk of heart failure, a 50% higher risk of heart disease and 7% increased risk of stroke and cerebrovascular disease compared to people of normal weight. The recommendation? Keep your waist measurement down to less than half of your weight (1).

Tapping in to the considerable effects of your gut microbiome on body weight

We live in symbiosis with the bacteria in our intestines and the complexity of the microbiome in our gut is only now being gradually revealed. One phenomenon that has been discovered is that both humans and animals can increase their stomach and intestinal motility if it is warranted. (Motility is the contraction of the muscles of the gastrointestinal tract that causes food to move through the digestive system.) For example, if food is scarce, motility is slowed to allow more time for calories to be absorbed. If food is plentiful, motility is increased. The gut bacteria have a major role in this signalling system and they do it through production of short-chain-fatty-acids (SCFAs). When SCFAs are plentiful, digestive motility is increased. Soluble fiber is the raw material that gut bacteria use to produce SCFAs. The more fiber eaten, the higher the gut motility, the faster food moves through the system and the fewer calories are absorbed. The standard Western diet provides an abundance of calories but little fiber. Good sources of soluble fiber include asparagus, onions, leeks, garlic, carrots, cucumbers, peppers, sweet potatoes, flaxseeds, chia seeds, tomatoes, bananas, berries, apples and legumes (2). A little boost in weight loss may be as simple as eating more of these healthy plant foods.

In addition to this, a hormone known as FIAF (Fasting Induced Adipose Factor) signals the body to stop storing fat and to start using it. This comes into play during fasting but could also be useful for weight loss. Some bacteria suppress this hormone (increasing fat storage) whereas the fiber-eating bacteria in our gut turn this hormone on (using up fat storage) (4). Once again, eating more soluble fiber can result in weight loss.

Another interesting aspect of the gut microbiome recently discovered is the significance of the bacterial species that are present in our microbiomes. Obesity is associated with changes in the relative abundance of the two dominant bacterial species in our gut, the Bacteroidetes and the Firmicutes . The obese gut has 50% more Firmicutes than Bacteroidetes species. One explanation for this finding is that Firmicutes produce more complete metabolism of a given energy source than do Bacteroidetes, thus promoting more efficient absorption of calories and subsequent weight gain (3,5). There is a class of phytonutrients called polyphenols in some foods that suppress the growth of Firmicutes while encouraging bacteroidetes (27). The healthiest sources of polyphenols are found in fruits such as apples, cherries, blueberries and grapes and vegetables such as onions and potatoes and green tea.

Influences on body weight begin much earlier than you might think…

Surprisingly, what a pregnant woman eats can permanently alter the biology of her children. Epigenetics is the study of how external factors can change the way genes are expressed. This science has discovered that when a mother experiences food shortage during pregnancy, her baby has a higher chance to be obese fifty years later. This is because the baby’s DNA is programmed before birth to expect famine. So called “thrifty” genes are turned on and they lead to conservation of calories at all costs. (6)

Similar effects can occur according to the type of protein a woman eats while pregnant. Eating protein from animal sources leads to increased body weight of the child by its 16th birthday. It has been discovered that every daily portion of meat intake during the third trimester seems to result in about one extra percent of body weight in the child, no matter how many calories the child eats or how much they exercise (7). This effect may be due to chemicals in meat called obesogens that stimulate the growth of fatty tissue. PAHs (Polycyclic Aromatic Hydrocarbons), are an example of these chemicals which are produced by cooking meat at high temperatures (frying or grilling). The more exposure a child has to PAHs, the more excess body weight they tend to have (8,9).

To sum up

If maintaining a healthy body and a healthy weight is your objective, keep in mind the old saying, “You can’t outrun the fork”. Combining the general health benefits of regular exercise along with a high fiber diet rich in whole-food plant-based sources is your best strategy for achieving success.


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2 Tropini, C., Earle, K.A., Casey, K. et al. The Gut Microbiome: Connecting Spatial Organization to Function. Cell Host and Microbe. Apr 2017; 21(4): 433-442.

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Promoting a healthy adventurous lifestyle powered by plants and the strength of scientific evidence.

My name is Debra Harley (BScPhm) and I welcome you to my retirement project, this website. Over the course of a life many lessons are learned, altering deeply-rooted ideas and creating new passions.

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