HIIT Sheds 25% Intra-Bellyfat in 32 Workouts - Despite T2DM & W/Out Dieting! Plus: Always 'Add Weights' When Dieting

High-intensity interval training (HIIT) sheds significantly more belly fat over (-10% vs. 0%) and under (-25% vs. +10%) female abs than isocaloric medium intensity steady state exercise aka MICT.

Losing 25% of visceral fat without dieting and with only two workouts per week (16 weeks x 2 workouts = 32 workouts total)? That sounds like straight from a 'spam ad' on Facebook, right? Well, it is based on scientific evidence, though... evidence from a study in Diabetes & Metabolism that tested the effects of a very manageable high-intensity interval training regimen (2 x 20 min per week) on abdominal fat mass in postmenopausal women with type 2 diabetes (Maillard. 2016).c

Ok, I have to admit that's different from both, (a) the athletes in the second study that made it into today's SuppVersity short news (the one about maximal fat oxidation) and (b) the average SuppVersity readers, but knowing the exact protocol, which is different from much (if not everything) you may have seen so far, alone, should be reason enough to read the rest of today's SuppVersity Short News (all short news | make sure to scroll down and click on "older news" at the bottom).
The former is particularly true since the scientists tested another, albeit non-HIIT training regimen, too, one that resembles what the seventeen women (69 ± 1 years; BMI: 31 ± 1 kg/m²) who participated in the study would probably have done if they had not been randomly assigned to the classic, but useless ...

• medium intensity cycling training (MICT) - 40 min at 55–60% of their individual HRR as calculated by (estimated HRmax − HRrest) × 0.55 (or 60%, respectively) + HRrest - instead of the previously hinted at
• high-intensity interval training (likewise cycling) HIIT program - 60 × 8 s at 77–85% HRmax, 12 s of active recovery (at 20–30 rpm) - that yielded impressive results

for only for 16 weeks with two isocaloric (= EEs per session did not differ between the two modalities (262 ± 58 kcal with HIIT and 240 ± 58 kcal with MICT; this is a difference to many previous studies, where, oftentimes, the steady state group burned more energy during their workouts) workouts per week. As promised in the headline, it did thus take as little as 32 workouts for the results to become measurable (via dual-energy X-ray absorptiometry) and visible - and that in spite of the lack of reductions in energy intake in both groups:

"Women were asked to maintain their normal eating habits during the 16-week study period. At baseline and at week 16 of training, each participant provided a 7-day food-intake diary, which was evaluated by a dietitian using nutrition analysis software (Nutrilog®, Marans, France)" (Maillard. 2016).

In addition, the subjects were "asked to maintain their normal levels of physical activity during the study period" (Maillard. 2016).
Now, I have to admit I haven't told about the importance of a small word in the headline yet. The word is "intra-" and points away from belly fat in general and towards the "intra-belly" visceral fat with it's unhealthy effect on blood lipids and glucose levels.

Figure 1: Body composition changes [based on dual-energy X-ray absorptiometry (DEXA) imaging] between baseline and end of the 16-week exercise program with MICT (n = 8) and HIIT (n = 8). Data are means ± SEM. MICT: moderate- intensity continuous training; HIIT: high-intensity interval training; FFM: fat-free mass; FM: fat mass; delta change (%) = [(16 weeks − baseline/baseline) × 100]. *P ≤ 0.05 (MICT vs. HIIT groups | Maillard. 2016).

With ~10%, though, even the total belly fat loss (visceral and subcutaneous) is remarkable. After all, there was (a) no dieting involved and (b) not even the slightest fat loss in the classic cardio group!
A group of which the data in Figure 1 tells you that the subjects who have been randomly assigned to do "their cardio" (MICT) even got 10.5±9.7 % fatter (viscerally, as measured by CT scans) over the course the 16-week study.

Figure 2: Lipid, fasting glucose and HbA1c changes from baseline to week 16 with moderate-intensity continuous training (MICT; n = 8) and high-intensity interval training (HIIT; n = 8 | Maillard. 2016).

Against that background, the scientists' observation that the 'bad' plasma triglyceride levels were higher with HIIT (group effect, P ≤ 0.05), while "overall, HbA1c and TC-to-HDL ratio both decreased after the intervention (time effect, P ≤ 0.05)" without significant inter-group differences. That sounds odd. As odd as the increase in fasting glucose. So what? Well, what is important, is that

"[...] the total cholesterol (TC) reduction was positively correlated with total visceral FM loss (r = 0.39; P ≤ 0.05) and HbA1c change was positively associated with the decrease in abdominal FM (r = 0.29; P ≤ 0.05)" (Maillard. 2016).

which points to an overall long-term benefit of HIIT on both, lipid and glucose metabolism. All that after 16 weeks, over which the scientists' nutrition and activity data confirm that the subjects did not - as they were advised - change their levels of physical activity (IPAQ score) or total energy (kcal) intake and macronutrient consumption (distribution and total amount).
References:

• Maillard, F., et al. "High-intensity interval training reduces abdominal fat mass in postmenopausal women with type 2 diabetes." Diabetes & Metabolism (2016).
• Weiss, P et al. "Effects of Weight Loss on Lean Mass, Strength, Bone, and Aerobic Capacity." Medicine & Science in Sports & Exercise: Post Acceptance: August 30, 2016 [ahead of print]. doi: 10.1249/MSS.0000000000001074.