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).

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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).

Whatever you do: If you want to lose weight - exercise! It's not just the study at hand that underlines how powerful (especially) HIIT exercise is when it comes to fat, not weight loss. Another recently published study by Edward P. Weiss et al. adds to the already convincing evidence that exercise protects you from the decreases in lean mass and reductions of VO2max that occur with deficits as low as only 20% (Weiss. 2016). In their study, Weiss et al. had observed that the ~2% (p=0.003) whole body and ~4% (p<0.0001) lower body lean mass loss that occurred during 15-18 weeks of dieting at 80% of the maintenance intake was reduced to non-significant 1% (p=0.44) and only just significant <2% (p=0.05) lower body lean mass loss while the ~6% decrease in aerobic exercise capacity was totally blunted with only 4.4+/-0.5 hr/wk of walking, jogging, cycling or more intense functional physical activities, such as yard work - needless to say that replacing that by a fast-paced strength training regimen (explicitly precluded in Weiss et al.) or concomitant strength + cardio training may have reduced the lean mass losses to zero, as well. 

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!

In January 2015 I wrote an article with the title "5 Reasons Why 50%+ of Your 'Cardio' Should Be HIIT". Now in 2016 the science is still valid | more

Beware of condemning MICT training! While you have read about the benefits (listed here) of doing HIIT before, there are also good sides of LISS and MICT. This is why I would like to remind you / prepare you for / a fact I highlight / will highlight in the bottom line, too: the study at hand shows nothing but the fact that in this subject group and (solely) for the purpose of losing visceral fat in the absence of dieting and, more importantly, in the absence of lifting weight, HIIT appears to be (albeit vastly) superior to an isocaloric bout (=you spend the same amount of energy training intensely and with intervals) ofsp steady state cardio (MICT).

If you lifted weight, for example, doing two types of exercise that tax the sympathetic nervous system may tax the CNS and produce results that are worse or not better than steady state cardio. Alternatively, if you lifted the calorie limit on the MICT, on the other hand, you may see (just as many previous studies did) that the extra calories burnt during MICT will help you lose more weight and often also more body fat. It's all about specificity and finding out what works for you!

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).

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Shouldn't the extreme visceral fat loss... trigger more significant improvements in 'bad' blood lipids (LDL) and glucose metabolism and by no means elevate triglycerides?

The latter is a valid question, but one you wouldn't ask if you were familiar with the effects of intense glycolytic training (HIIT, sprints, weights, etc.) on triglyceride levels, which are increased, because (a) HIIT & co will increase the amount of fat that is released from the fat cells (esp. after the workouts), while they (b) burn less fat than "classic cardio" during the workouts. To consider that "health-damaging" would thus be unwarranted.

And while I cannot explain, though, is why we don't see more significant improvements in the blood lipid composition of the HIIT group, I do know that (a) this is likewise a result, scientists have previously observed in scientific studies and that (b), and more importantly, none of the inter-group differences (including the nasty increase in LDL) was statistically significant (in fact, the p - values were all p > 0.5 [no typo], when p < 0.05 would signify statistical significance).

Overall, the studies main and only message is thus exactly what you've read in the headline: You can lose highly significant and significantly more belly fat (not total body fat, where both groups lost the same 1-2% of their total fat mass | another potential explanation for the lack of sign. differences as far as health benefits are concerned) if you invest 2x20 minutes into HIIT training per week compared to "classic steady state cardio" aka MICT. That's the message of the study - a message I would like to complement with (a) the advice from the light blue box, i.e. "Whenever you're tryin' to lose weight, do resistance training, too. Your muscles will thank you!", and (b) the reminder that this is a single study with an important limiter that is not always valid in the real world, i.e. identical energy expenditure in both arms of the study, if that's not guaranteed (and usually people burn more during "cardio" than during HIIT (including its aftermath)) the HIIT advantage you see in this study may easily melt away | Comment!

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.