High intensity interval training (HIIT) has been reported to be effective, well-tolerated and a more powerful stimulus than traditional moderate intensity exercises in reducing cardiometabolic disturbances (e.g., blood pressure, lipid profile and insulin resistance) and increasing cardiorespiratory fitness levels in different at risk populations with cardiometabolic diseases [ 11 13 ]. Thus, a critical question that remains unresolved is whether HIIT could protect the cardiometabolic profile against the potential negative effects of a fast food diet. Knowledge on the effect of a fast food diet in combination with HIIT on the cardiometabolic profile may help us better understand the risk of disease of an individual and as such provide useful information to health professionals. Therefore, the purpose of the present study was to investigate the role of HIIT during a fast food diet on cardiometabolic risk factors in young healthy men. We hypothesized that HIIT would protect the cardiometabolic profile against the potential negative effects of a fast food diet. Specifically, we hypothesized that insulin resistance (the HOMA index as primary outcome), fasting glucose and insulin as well as the lipid and inflammation profile (as secondary outcomes) would not deteriorate after the intervention.

In the general population, there is a popular belief that fast food consumption is generally recognized to be unhealthy irrespective of the calories ingested or the levels of physical activity of an individual. This is not a trivial argument. Interestingly, a recent study showed that short term (seven days) overfeeding (50% increase in energy intake) combined with a reduction in physical activity (<4000 step/day) was associated with a decrease in insulin sensitivity in young healthy men. However, when daily continuous running on a treadmill at a high intensity (45 min at 70% VOmax) was added, this was able to offset the deterioration in insulin sensitivity despite an energy surplus [ 10 ]. This provides tantalizing evidence of the protective effects of daily high intensity exercise.

The consumption of fast food has considerably increased during the last few decades [ 1 3 ]. There is evidence to suggest that 36% of US adults consume fast foods during any day of the week [ 2 ]. In fact, during 2007–2010, US adults consumed ~11% of their total daily energy intake from fast foods [ 4 ]. In addition, several studies have shown that frequent consumption of fast foods may be associated with weight gain [ 5 7 ] and cardiometabolic complications [ 7 8 ]. Indeed, Alhéritière et al. [ 9 ] reported a strong positive correlation between the number of McDonald’s restaurants and the prevalence of overweight individuals across 44 countries.

2. Materials and Methods

Participants: Sixteen participants were recruited in this interventional study between June 2015 and March 2016 using advertisement via emails and short presentations in classrooms at the Université du Québec à Montréal. Participants were included in the study if they met the following criteria: (1) male; (2) aged between 18–30 years old; (3) a body mass index (BMI) between 18.5–29.9 kg/m2; (4) physically active (>150 min of physical activity/week), no orthopedic limitations, non-smoker; and (5) low alcohol consumers (≤1 drink/day). Exclusion criteria were: (1) chronic diseases such as cardiovascular disease, diabetes and cancer, (2) currently following a fast food diet; (3) gastrointestinal problems such as bloating, nausea, indigestion, constipation and diarrhea. All participants lived in the Montreal region and spoke French and that the majority (87%) were University students with a low personal annual income (< $ 20,000) and were not married. The study was conducted in accordance with the Declaration of Helsinki and all procedures were approved by the Ethics Committee of the Université du Québec à Montréal (Trial registration: A-140063). All participants were fully informed about the nature, goal, procedures and risks of the study, and gave their informed consent in writing.

Procedure: A phone interview was conducted to screen for the aforementioned inclusion/exclusion criteria. After screening, each participant was invited to the Department of Exercise Science at the Université du Québec à Montréal in the fasting state at 8:00 a.m. for a series of tests. Upon their arrival, blood sampling, anthropometric, body composition, blood pressure and estimated maximal oxygen consumption measurements were performed. The exercise and dietary intervention began 48 h after metabolic testing. Furthermore, during the intervention a SenseWear armband was placed on the participant for the measurement of energy expenditure. Post testing was performed after 48 h of the last training session.

Blood samples: After an overnight fast (12 h), venous blood samples were collected and analyzed on the day of collection. Analyses were performed on the COBAS INTEGRA 400 analyzer (Roche Diagnostics, Laval, QC, Canada) for total cholesterol, HDL-cholesterol, triglycerides, glucose, aspartate aminotransferase (AST), alanine aminotransferase (ALT) and gamma-glutamyltransferase (GGT). LDL-cholesterol was calculated from the Friedewald equation [ After an overnight fast (12 h), venous blood samples were collected and analyzed on the day of collection. Analyses were performed on the COBAS INTEGRA 400 analyzer (Roche Diagnostics, Laval, QC, Canada) for total cholesterol, HDL-cholesterol, triglycerides, glucose, aspartate aminotransferase (AST), alanine aminotransferase (ALT) and gamma-glutamyltransferase (GGT). LDL-cholesterol was calculated from the Friedewald equation [ 14 ]. Insulin levels were quantified in duplicate using a human insulin radioimmunoassay (Linco Research, Inc., St-Charles, MO, USA). Homeostasis model assessment (HOMA) = fasting insulin x fasting glucose/22.5 was then calculated [ 15 ]. Glycated hemoglobin (HbA1c) levels were measured by HPLC using the D-100 analyzer (Bio-Rad, Montreal, QC, Canada). Serum lipoprotein(a) (Lp(a)), apolipoprotein B (apoB) and high sensitivity (hs) C-reactive protein (hsCRP) were assessed by immunonephelometry on IMMAGE analyzer (Beckman-Coulter, Villepinte, France).

Body composition: Total body weight, fat mass, body fat percentage and lean body mass were measured using dual energy X-ray absorptiometry (General Electric Lunar Prodigy; standard mode; software version 12.30.008, Madison, WI, USA). Calibration was executed daily with a standard phantom prior to each test. In addition, standing height (±0.1 cm) was measured using a wall stadiometer (Perspective Enterprises, Michigan, USA). BMI = Body weight (kg)/Height (m2) was then calculated. Waist circumference was measured to the nearest 0.5 cm by using a non-elastic plastic tape with the participant standing upright.

Blood pressure: Systolic and diastolic sitting blood pressure was determined by an automatic sphygmomanometer machine (Spot Vital Signs® Devices, Welch Allyn, Mississauga, ON, Canada). An appropriate cuff size was selected for each participant based on arm circumference. Conditions were carefully standardized: no talking, cuff on the left arm and 5 min of rest. Two measurements with 3 min of rest between measures were taken. The average of the two measures was reported.

Estimated maximal oxygen consumption (VO 2 max): The Bruce Protocol on the treadmill was used to evaluate maximal oxygen consumption (VO 2 max) [ 2 max was calculated using the following validated prediction equation for men [ 2 max (mL/kg/min) = 14.76 − (1.379 × T) + (0.451 × T2) − (0.012 × T3), where T = maximum time on the treadmill in minutes. The Bruce Protocol on the treadmill was used to evaluate maximal oxygen consumption (VOmax) [ 16 ]. The first stage began at a treadmill speed of 2.7 km/h and an incline of 10% gradient for 3 min. Thereafter, there was a progressive increase in the level of intensity (inclination and speed) every 3 min until voluntary exhaustion was reached. Maximal heart rate was recorded at exhaustion. The estimated VOmax was calculated using the following validated prediction equation for men [ 17 ]: VOmax (mL/kg/min) = 14.76 − (1.379 × T) + (0.451 × T2) − (0.012 × T3), where T = maximum time on the treadmill in minutes.

Dietary intervention: For 14 consecutive days, participants were subjected to an exclusive fast food diet from a popular fast food restaurant chain located in the Montreal area. Volunteers had to consume an extra value meal of their choice for breakfast, lunch and dinner. All meals for lunch and dinner consisted of a sandwich (e.g., Big Mac®, McChicken®, or Quarter Pounder with Cheese®), medium fries and a non-diet medium soft drink. As for breakfast, it consisted of a sandwich (e.g., Egg McMuffin®, or Sausage McMuffin®), hash browns and a small fruit drink or coffee. In addition, participants had the option to consume a muffin of their choice as a snack depending on their appetite. Each subject received a gift card to purchase all meals. Participants had to provide all receipts of the meals they had purchased to the researchers on a daily basis. This allowed determining exactly all of the foods each subject ingested. Dietary analyses were then conducted using the popular restaurant chain Nutrition Center’s website to determine total daily intake of protein, carbohydrate, fat, saturated fat, trans fat and sodium levels as well as total energy intake. In addition, all gastrointestinal problems such as bloating, nausea, indigestion, constipation and diarrhea were documented daily during the 14-day intervention. Each participant was instructed not to consume any other foods during the study. It should also be noted that a 2-week dietary intervention or less has been shown to be sufficient in inducing negative changes to the metabolic profile [18,19,20, For 14 consecutive days, participants were subjected to an exclusive fast food diet from a popular fast food restaurant chain located in the Montreal area. Volunteers had to consume an extra value meal of their choice for breakfast, lunch and dinner. All meals for lunch and dinner consisted of a sandwich (e.g., Big Mac, McChicken, or Quarter Pounder with Cheese), medium fries and a non-diet medium soft drink. As for breakfast, it consisted of a sandwich (e.g., Egg McMuffin, or Sausage McMuffin), hash browns and a small fruit drink or coffee. In addition, participants had the option to consume a muffin of their choice as a snack depending on their appetite. Each subject received a gift card to purchase all meals. Participants had to provide all receipts of the meals they had purchased to the researchers on a daily basis. This allowed determining exactly all of the foods each subject ingested. Dietary analyses were then conducted using the popular restaurant chain Nutrition Center’s website to determine total daily intake of protein, carbohydrate, fat, saturated fat, trans fat and sodium levels as well as total energy intake. In addition, all gastrointestinal problems such as bloating, nausea, indigestion, constipation and diarrhea were documented daily during the 14-day intervention. Each participant was instructed not to consume any other foods during the study. It should also be noted that a 2-week dietary intervention or less has been shown to be sufficient in inducing negative changes to the metabolic profile [ 10 21 ].

Exercise intervention: The high intensity interval training (HIIT) program was performed daily for 14 consecutive days on the treadmill. Each exercise session consisted of a 5 min warm-up, followed by 15 × 60 sec sprint intervals (~90% of maximal heart rate) interchanged with 60 sec active recovery (walking) and ended with 5 min cool-down. All exercise sessions were supervised by a kinesiologist and were performed at the Department of Exercise Science at the Université du Québec à Montréal. The HIIT program was adapted based on a previous study [ The high intensity interval training (HIIT) program was performed daily for 14 consecutive days on the treadmill. Each exercise session consisted of a 5 min warm-up, followed by 15 × 60 sec sprint intervals (~90% of maximal heart rate) interchanged with 60 sec active recovery (walking) and ended with 5 min cool-down. All exercise sessions were supervised by a kinesiologist and were performed at the Department of Exercise Science at the Université du Québec à Montréal. The HIIT program was adapted based on a previous study [ 22 ]. It should be noted that each participant was instructed not to perform any sports or other strenuous exercises during the study.

Energy expenditure: Total and physical activity energy expenditure as well as energy expenditure during HIIT were evaluated for 14 consecutive days using the portable mini SenseWear armband (Bodymedia, Pittsburgh, PA, USA). The portable armband uses a 3-axis accelerometer, a heat flux sensor, a galvanic skin response sensor, a skin temperature sensor, and a near-body ambient temperature sensor to capture data. These data as well as body weight, height, handedness and smoking status (smoker or non-smoker) are used to calculate energy expenditure. The armband was placed on the upper left arm (on the triceps at the mid-humerus point) of each volunteer. All participants were instructed to remove the armband only for bathing purposes or any water activity. The net output is a measure of energy expenditure (kilocalories) utilized by the participant across time. Data were extracted using the SenseWear professional software 8.1 (Bodymedia, Pittsburgh, PA, USA). This method of energy expenditure measurement has been validated by several studies [24, Total and physical activity energy expenditure as well as energy expenditure during HIIT were evaluated for 14 consecutive days using the portable mini SenseWear armband (Bodymedia, Pittsburgh, PA, USA). The portable armband uses a 3-axis accelerometer, a heat flux sensor, a galvanic skin response sensor, a skin temperature sensor, and a near-body ambient temperature sensor to capture data. These data as well as body weight, height, handedness and smoking status (smoker or non-smoker) are used to calculate energy expenditure. The armband was placed on the upper left arm (on the triceps at the mid-humerus point) of each volunteer. All participants were instructed to remove the armband only for bathing purposes or any water activity. The net output is a measure of energy expenditure (kilocalories) utilized by the participant across time. Data were extracted using the SenseWear professional software 8.1 (Bodymedia, Pittsburgh, PA, USA). This method of energy expenditure measurement has been validated by several studies [ 23 25 ].