There are two types of fat which people are concerned with losing. Visceral fat surrounds your internal organs, like the intestines. When you see someone with a huge gut, that’s visceral fat. This type of fat is relatively easy to lose with a sensible diet & exercise.
Subcutaneous fat is the ‘stubborn fat’ that stays, even through dieting & regular exercise. It becomes even more difficult to remove after the human athletic peak (around) age 27.
There is much literature on ‘stubborn fat’ and much of the science is recognized.  But what actually causes this fat to be so stubborn? I propose the answer is: hip & back injuries which people don’t recognize they have, until it’s too late.
Women tear their hip, abdominal and back muscles during childbirth, so this pertains to all mothers. 
Everything thing we physically do starts with our hips & back, and these are the most powerful skeletal muscles in the human body. They are also often the most neglected. You never hear any barbell guys in the gym say, “I’m going to work my lower back and hip stabilizers today.”
Other athletes are the same way, focusing too much on arms & legs, and not enough on their core– which means hips, back & abdominals. These are the muscles that true athletes maintain throughout their lives.
If these groin injuries aren’t properly & completely rehabilitated, then a semi-paralysis of the mid-section ensues. This injury victim will not be able to rotate their spine freely in the affected vertebrae, which are located in the lower back. This leads directly to weight (fat) gain. Other common issues become incontinence, colon cancer, and loss of virility.
The skin around stubborn fat becomes cold & lifeless. This is because there is no muscular activity, therefore little bloodflow to these areas. This is the pooch gut, love handles, cottage cheese thighs & butt, and back fat which honestly are disgusting. The injury victim will not be able to activate these areas because the deep muscles are torn, and atrophy has set in on the superficial muscles as well. The victim needs to focus on activating the deep injury, gently at first, then more actively & aggressively, but always under control. If done with persistent focus & vigilance, these muscles can be rebuilt and reinforced in a short period of time.
This will allow the injury victim to regain a youthful gait & look, as compared to most who limp & slump into middle age & beyond. These ‘dead backs’ exist in ~80% of the U.S. population, by my casual inspection. This means tens (hundreds?) of millions of American adults are suffering (right now) from an undiagnosed apophyseal avulsion fracture. The most common hip injury locations are shown below:
The apophysis is the projection on the spine that links the brain & spinal cord (CNS) to every skeletal muscle. This is what is fractured, as the hip muscles are torn from the bone.
Victims of an apophyseal avulsion fracture should be able to recall a specific event that triggered the pain; a traumatic injury on the sports field, playground, gym class or while alone. In children, adolescents & teenagers these injuries occur so frequently, and are often dismissed as ‘minor tweaks,’ so they often remain undiagnosed into adulthood.
The pain is most severe during activity and improves with rest. Tenderness can be appreciated by palpation, and the injury victim may actively guard against contraction of the musculature attached to the injured apophysis. Passive stretch of these muscles will reproduce the pain. 
The injury victim will recover (somewhat), but he/she will never be the same. Their strength and coordination will be eroded by this deep groin/back injury, which limits and restricts certain directional movements. Over time (years/decades), these injuries become disabling to those who don’t deal with them directly.
Into adulthood, a limp will often present itself, and there is a noticeable atrophy in the muscle group attached to the avulsed apophysis compared to the contralateral side. 
Hip fractures are common in the elderly, and often attributable to these injuries. The atrophied hip muscles leave only skin & bone, with fatty protection. Elderly men & women fall everyday and never get up.
An atrophied hip has no muscle tissue to protect the femoral arteries, and many geriatric hip fractures slice this vital vessel. The injury victim can bleed out in seconds.
This ignoble fate can be avoided by rehabilitating & strengthening your hips for life. The knowledge is here, but you must have the most serious dedication because this injury is very deep, meaning true rehabilitation will be intense & painful. It will take a period (weeks/months) for successful and complete activation of this atrophied muscle tissue, buried in stubborn fat.
Stubborn fat is a protective mechanism. Since the injury victim didn’t rehabilitate their injury, a layer of fat is deposited to protect the muscle from further injury. This causes the muscle to atrophy over time– since it can’t be used until healed. If it never heals, the stubborn fat remains.
Once the injury victim reactivates this long-atrophied muscle tissue, new muscle can quickly be rebuilt, and the stubborn fat in that area will melt away. This means that when the injury victim finally fixes all the torn muscles in their back, hips & abdominals (deep to superficial & back again), then all their stubborn fat will disappear. This is the best weight-loss program, as it is natural with no PED’s or crazy diets. I do recommend marijuana for the pain, as you’ll likely need something. It’s the most organic choice, and easiest to quit when you’re finished.
Note that you must maintain a calorie deficit to lose weight. You need plenty of sleep to lose fat, as that’s the primary fat burning period (diagram above). Eat a sensible whole food diet, that is high in fresh vegetables (juicing) with minimal lean protein, as most of the amino acid building blocks will come from your stubborn fat burn-off. Carbohydrates should be (mostly) organic and minimal, for energy boost and craving relief. Imagine this to be your normal diet, just in smaller proportions until you lose all of your stubborn fat.
Once you are truly lean & healthy, you will see life in a new way. Your thinking will be sharper and eyesight clearer. Former injury victims will now feel many years/decades younger, with more power, better coordination and longer stamina. Future injury-risk is sensibly minimized with a complete rehabilitation of these nasty hip/back injuries. The alternative is more pain & suffering. 
It’s not really a choice, once you know what to do– so do it now.