Aerobic exercise in the form of walking, running or swimming is the type of activity most often prescribed by physicians and physical educators for the prevention and treatment of diseases associated with obesity and unhealthy eating habits.
However, a Brazilian study published in the journal Life Sciences shows that resistance training in rats – similar to muscle building or functional training in humans – can also prevent the cardiovascular and metabolic alterations induced by a fat-rich diet, although when practiced at moderate intensity, as in the study, it does not avoid weight gain.
The experiments with rats were part of Guilherme Speretta’s PhD research, supported by a scholarship from FAPESP and supervised by Débora S. A. Colombari, a professor at São Paulo State University’s Araraquara School of Dentistry (FOAr-UNESP).
“In sedentary animals, we found that the high-fat diet modified gene expression and made them more predisposed to hypertension,” Colombari said. “In the group subjected to resistance training that didn’t happen even with an unbalanced diet.”
A previous experiment designed to measure the effects of a high-fat diet in the laboratory compared two groups of sedentary rats: a control group that received a standard diet (typical rat chow) containing 4 grams of fat per 100 g and a second group fed a diet with four to five times more fat.
“The high-fat diet consisted of standard chow plus peanuts, milk chocolate and sweet biscuits in proportions previously established in the scientific literature,” Colombari said. “The mixture makes the high-fat diet palatable and raises its energy content from 2.25 kilocalories per gram to 3.8 kcal/g.”
This difference, in conjunction with the palatability of the diet, mimics modern-life situations in which high caloric intake by children and adults puts their health at risk. “Physical activity undoubtedly improves cardiovascular and metabolic performance, but the effects of exercise must be accompanied by dietary reeducation,” she added.
After six weeks, the group that received the high-fat diet already displayed a sustained increase in heart rate (30 bpm) and mean arterial pressure, which was 10-15 millimeters of mercury (mmHg) higher than that of the control group.
“This higher arterial pressure in rats fed the high-fat diet already made them pre-hypertensive or even hypertensive,” Colombari said.
A more significant finding, however, was the impairment of baroreflex function in rats fed the high-fat diet. The arterial baroreflex via the central nervous system is one of the body’s homeostatic mechanisms and plays an important role in short-term regulation of blood pressure.
“When arterial pressure rises for whatever reason, the baroreflex is rapidly activated and induces dilation of resistance blood vessels, a decrease in heart rate, and several other changes that bring blood pressure back to normal,” Colombari said. “When this mechanism is impaired, reflex adjustment of arterial pressure doesn’t occur efficiently.”
When they analyzed gene expression in the animals’ brains, the researchers observed alterations in the nucleus of the solitary tract, a group of brain cells involved in the autonomic regulation of blood pressure and baroreflex control.
“In the animals fed the high-fat diet, we observed an increase in pro-hypertension components of the renin-angiotensin system, such as the AT1 receptor and angiotensin-converting enzyme, or ACE,” Colombari said. “On the other hand, there was less expression of components of the hypotensive or protective pathway of this system, such as the AT2 receptor. This combination increased their propensity to hypertension.”
The renin-angiotensin system is a cascade of peptides, enzymes and hormone receptors that acts as a critical regulator of sodium balance, extracellular fluid volume, vascular resistance and arterial blood pressure.
Effects of resistance training
The next step was to find out what would happen if the animals began resistance training before being fed a high-fat diet and continued to train once that unhealthy diet began. The new experiment involved four groups of rats: sedentary with a standard or high-fat diet and submitted to resistance training with either diet.
The rats trained by climbing a vertical ladder with a load fixed to their tails. “Before training began, we measured each animal’s maximum carrying capacity to ensure they exercised with the same relative intensity, which corresponded to 50-60% of the maximum,” Colombari explained. “Because increasing strength is one of the adaptations induced by this type of exercise, we performed new tests every two weeks to maintain the relative intensity throughout the training period.”
The rats were trained three times a week for ten weeks to find out whether this type of exercise was capable of offsetting the effects of the high-fat diet. In the first three weeks, all the animals received the standard diet. In the following seven weeks, the high-fat diet was given to two groups, one sedentary and the other active, and all the animals were evaluated at the end of the period.
Body weight and adipose tissue increased by approximately 150 g during the ten-week period in both groups fed the high-fat diet. Only the group that remained sedentary exhibited a rise in total cholesterol, fasting blood sugar, heart rate and mean arterial pressure as well as baroreflex impairment. Impaired insulin sensitivity, a precursor to diabetes, was also observed in this group at the end of the training period.
“In the group submitted to resistance training, all these metabolic variables remained similar to those of the control animals that received the standard diet, whether sedentary or trained,” Colombari said. “Solitary tract renin-angiotensin system component gene expression also remained the same as in the control animals.”
The analysis of gene expression also pointed to significant chronic inflammation in the solitary tract of the sedentary animals that received the high-fat diet. “We observed an increase in the expression of inflammatory cytokines such as interleukin-1β and tumoral necrosis factor-α and a decrease in interleukin-10 in the solitary tract,” Colombari said. “No such inflammation was observed in the trained animals.”
Another difference that the researchers found was sympathetic blood vessel modulation, which is controlled by the central nervous system. This variable was higher in sedentary rats fed the high-fat diet, suggesting a possible increase in peripheral resistance to blood flow, which, according to Colombari, is a crucial factor in the development and maintenance of hypertension.
“In trained animals that received the high-fat diet, sympathetic modulation was equal to that in the control group,” she said. “This is possibly why their arterial pressure didn’t rise.”
In Colombari’s opinion, the data presented in the article reinforce the importance of physical exercise in preventing the harmful effects of an unhealthy diet. “Most people only start doing physical exercise after they’ve already discovered a health problem,” she said. “Our study underscores the importance of prevention.”
According to Colombari, most scientific studies of this topic focus on the benefits of aerobic exercise, which consumes more energy and reduces body mass. “But we show that resistance training also has important benefits. Ideally, of course, people should do both kinds of exercise.”